Convolvulaceae

A. R. G., Simões, G., Huerta-Ramos, A. L. C., Moreira, J. R. L., Paz, J., Grande Allende, P., Pisuttimarn, P., Rattanakrajang, J. C. J., Barbosa, R., Simão-Bianchini, R. K., Kojima, C. P., Paixão, M., Declercq, S. P., Kagame, J. A., Luna, M. R., Pace, C., Alcantara, B. D., Williams, L. O., Duque, V., Gowda, V. B., Shimpale & Eserman, L., 2024, Sweet potato, morning glories, bindweeds: an overview of Convolvulaceae, Rheedea 34 (5), pp. 267-308 : 273-288

Key advances in Convolvulaceae research

3.1 Systematics: the era of molecular phylogenetic analyses and the outstanding challenges Convolvulaceae are classified in the order Solanales , as earlier proposed by traditional morphological classification systems ( Cronquist, 1988; Dahlgren, 1989; Thorne, 1992) and reinstated by molecularbased classifications ( APG IV, 2016; Zuntini et al., 2024), being sister to Solanaceae (the family of nightshades, tomato, potato, eggplants), along with Montiniaceae , Sphenoclaeceae, and Hydroleaceae . The order Solanales belongs in the supra-order Lamiids, which also encompasses Lamiales and Boraginales ( APG IV, 2016) . Convolvulaceae can be distinguished from other families in the Solanales by the presence of laticifers, intraxylary phloem (likely shared with Solanaceae ), common presence of successive cambia, and a set of unique seed and pollen morphological traits (Stevens, 2001). Takhtajan (1997) proposed the recognition of Convolvulaceae as a separate order,Convolvulales, based on these characters. It is the only family in the Asterid clade where seeds show physical dormancy (Jayasuryia et al., 2008, 2009; Gunadasa et al., 2024). Convolvulaceae also produce diverse critical secondary metabolites such as tropane alkaloids, and this trait is shared with its sister family Solanaceae ( Eich, 2008) . Despite several morphological coherence within Convolvulaceae , some authors have disputed this, and recognised new families such as Cuscutaceae , Dichondraceae , and Humbertiaceae from Convolvulaceae (Austin, 1973) , thus splitting the family. The introduction of molecular phylogenetic analyses has come to demonstrate that Convolvulaceae is monophyletic, with the inclusion of Cuscuta , Dichondra and Humbertia , and therefore these genera should not be recognised as segregate families (Stefanović et al., 2002, 2003; Simões et al., 2022; Zuntini et al., 2024).

Within Convolvulaceae , classification at subfamily and tribal level has also varied significantly between authors and over time, depending on the hierarchical value of the characters chosen to differentiate these higher-level divisions, for example: fruit type, ovary characters, style and stigma shape and number, etc. The first proposal of a supra-generic classification within Convolvulaceae was made by Choisy (1834), who created four “sections”: Argyreieae - characterised by a syncarpous gynoecium and indehiscent fruits; Convolvuleae - characterised by a syncarpous gynoecium and dehiscent fruits; Dichondreae – presence of an apocarpous gynoecium and dehiscent fruits, and finally Cuscuteae - characterised by their parasitic life form. Later, Choisy (1845) re-ranked these “sections” as tribes, while retaining the names and the circumscription.

Another classification was later proposed by Hallier (1893), dividing the family into two ‘subfamilies’ based on the morphology of pollen grains: 1) Echinoconieae (including two tribes), characterised by pollen grains with echinate (spiny) exine, and 2) Psiloconieae (including seven tribes), characterised by pollen grains with psilate (non-spiny) exine. Later, Van Ooststroom (1953), classified Convolvulaceae into the subfamilies Cuscutoideae (composed solely of the tribe Cuscuteae ), and Convolvuloideae (which included the tribes Convolvuleae and Ipomoeeae ). The first phylogenetic analyses were introduced by Austin (1973, 1988), who proposed a cladogram based on morphological and cytological characters. From this phylogenetic proposal, he recognised nine tribes: Argyreieae , Ipomoeeae , Convolvuleae , Cuscuteae , Erycibeae , Hidebrandtieae, Cresseae, Poranae , and Dichondreae , as well as the doubtful group that he coined as ‘Merremioids’ (Austin, 1982).

The incorporation of molecular data into phylogenetic studies (Stefanovic et al., 2002, 2003) has come to help settle the subfamily and tribal level classifications and has shown the systematic value of stigma and style characters, as synapomorphies at this taxonomic level (Table 1). For example, the division of Hallier (1893) based on pollen characters was proved consistent with the molecularphylogenetic results, with Echinoconieae resolved as monophyletic. Therefore, while molecular evidence has come to re-shape the higher-level classification of the family, it has also confirmed the systematic value of micromorphological characters used in past classifications, namely style, stigma and pollen, and reinforced their predictive value for systematic relationships.

Molecular phylogenetic studies have also offered greater clarity in tribal circumscription, confirming that some of the previously defined tribes were monophyletic, e.g. Convolvuleaee and Cuscuteae , while others needed to be re-circumscribed or needed further investigation, e.g. Cresseae , Poraneae or the “problematic” Merremieae (Stefanović et al., 2002, 2003). An integrative approach has been taken to re-evaluate the circumscription of tribe Merremieae and its genera, resulting in an improved classification with monophyletic genera, morphologically and micromorphologically diagnosable genera, while the tribe itself was demonstrated to be polyphyletic, non morphologically diagnosable, and was dissolved (Simões et al., 2015; Simões & Staples, 2017). The ambiguous generic placement of particular species has also been clarified by a combination of molecular and micromorphological evidence (Tamboli et al., 2021; Pisuttimarn et al., 2023). More recently, nuclear genomic data (Simões et al., 2022; Zuntini et al., 2024) has been helpful to resolve uncertainties in tribal delimitation and generic placement, for example suggesting for the first time a close relationship of genus Distimake with tribe Ipomoeeae , in a completely new relationship never hypothesised in previous studies, but otherwise confirming most of the known subfamily and tribal delimitations. At present, the circumscription of tribes Cresseae and Poraneae remain the least well established, and the position of the genera Cuscuta and Erycibe within the family is yet unresolved (Simões et al., 2022). The dissolution of tribe Merremieae has also left nine genera unclassified at tribal level, and treated as “ incertae sedis ”, pending further studies.

In general, the higher-level relationships within Convolvulaceae are among the biggest challenges yet to be overcome in this plant family. Even though most of the circumscriptions of subfamilies and tribes are stable in the most part, the uncertainty of the position of key genera such as Cuscuta and Erycibe , the uncertain classification of some of the “Merremioids”, and the lack of support in the relationships between tribes themselves, means that a full re-classification of the family is not yet possible. This lack of a “phylogenetic backbone” also hinders broader scale evolutionary and biogeographic analyses.

The ongoing work is an integrative taxonomic approach by combining molecular phylogenetic toolswithmorphologicaldata towards an improved subfamily and tribal level classification of the family. However, this effort is hindered mostly by incomplete sampling or the need of morphological data from a wide geographic region, as many of the genera and tribes span across different continents. An international collaborative effort is being coordinated to not only extensively sample DNA from all the Convolvulaceae genera across different biogeographic regions, but also to extensively morphologically, micromorphologically, geographically and ecologically characterise them, so that significant progress can be made in this sense.

3.2. Large genera vs diagnosable genera? A turning point for generic re-classification The era of molecular phylogenetics has helped to successfully re-assess the circumscription of subfamilies and tribes and re-interpret the systematic value of traditionally used morphological and micromorphological characters. This is also true for traditionally recognised genera, especially the most

Table 2. Summary of Convolvulaceae Classification (based on Stefanović et al., 2002; POWO, 2024). *The name “ Dichondroideae ” is here applied to refer to the clade Dicranostyloideae (“bifid clade”), which has been lacking a formal recognition as subfamily since the phylogenetic revision of the classification of the family (Stefanović et al., 2002; Stefanović & Olmstead, 2003). A new revision of the classification of the family is ongoing which may revisit the nomenclature of the subfamiliar and tribal divisions currently recognised.

Rank Name Species Distribution

Subfamily CUSCUTOIDEAE 220 Temperate, Tropics & Subtropics Tribe Cuscuteae 220 Temperate, Tropics & Subtropics Genera Cuscuta 220 Temperate, Tropics & Subtropics Subfamily Tribe Genera HUMBERTIOIDEAE Humbertieae Humbertia 1 1 1 Madagascar Madagascar Madagascar Subfamily Tribe Genera ERYCIBOIDEAE Erycibeae Erycibe 73 73 73 Asia, Australia Asia, Australia Asia, Australia Subfamily Tribe Genera CARDIOCHLAMYDEAE Cardiochlamyeae Cardiochlamys 24 12 2 Asia, Australia, Madagascar, C. America Asia, Madagascar Madagascar Cordisepalum 2 Asia Dinetus 8 Asia Tribe Genera Poraneae Duperreya 12 3 Asia, Australia, Madagascar, C. America Australia Poranopsis 3 Asia, Australia, Madagascar, Central America Tridynamia 4 Asia Porana 2 Asia, Mexico Subfamily Tribe Genera DICHONDROIDEAE * Cresseae Bonamia 439 249 70 Temperate, Tropics & Subtropics Temperate, Tropics & Subtropics Tropics Cladostigma 3 NE. & E. Tropical Africa, SW. Arabian Peninsula Cressa 5 Temperate & Subtropics Evolvulus 106 Tropics & Subtropics Hildebrandtia 11 NE. & E. Tropical Africa, Arabian Peninsula, Madagascar Itzaea 1 S. Mexico to Central America Neuropeltis 14 West & Central Africa, Asia Neuropeltopsis 1 Borneo Seddera 28 Africa, Arabian Peninsula, India Stylisma 7 Central & East USA

Rank Name Species Distribution

Wilsonia 3 Australia Tribe Dichondreae 47 Africa, Tropical & Subtropical America, Australia, Madagascar South Tropical America, West & Central Africa Genera Calycobolus 18 Dichondra 15 W. & S. U.S.A. to Tropical & Subtropical America, Mascarenes, Australia, New Zealand Dipteropeltis 2 West & Central Africa Falkia 3 Arabian Peninsula, Eritrea to S. Africa Metaporana 6 E. Central & E. Tropical Africa, Socotra, Madagascar Nephrophyllum 1 NE. Tropical Africa Petrogenia 1 Texas to NE. Mexico Rapona 1 Madagascar Tribe Genera Jacquemontieae Jacquemontia 106 106 Tropics & Subtropics Tropics & Subtropics Tribe Genera Maripeae Dicranostyles 37 16 Central & S. Tropical America Central & S. Tropical America Lysiostyles 1 N. South America to N. Brazil Maripa 20 SE. Mexico to S. Tropical America Subfamily Tribe Genera CONVOLVULOIDEAE Convolvuleae Convolvulus 1,198 240 203 Temperate, Tropics & Subtropics Temperate & Subtropics Temperate & Subtropics Calystegia 26 Temperate & Subtropics Polymeria 11 Lesser Sunda Islands to Australia, New Caledonia Tribe Genera Aniseieae Aniseia 6 3 Tropical & Subtropical America Tropical & Subtropical America Odonellia 2 Mexico to South Tropical America Tetralocularia 1 South Tropical America Tribe incertae sedis / “ Merremieae ” Merremia s.s. 137 10 Asia, Australia Merremia s.l. 34 Africa, Asia Distimake 46 Tropics & Subtropics Decalobanthus 19 E. Africa, Madagascar, Tropical Asia to Pacific

Rank Name Species Distribution

Hewittia 1 Tropical Africa and Tropical Asia Hyalocystis 2 NE. Tropical Africa Xenostegia 6 Tropical Africa, Tropical Asia & Australia Remirema 1 Thailand Operculina 13 Tropical America, Africa, Asia, Australia & Pacific Camonea 4 Tropics & Subtropics Daustinia 1 Brazil Tribe Ipomoeeae Argyreia 815 143 Tropics & Subtropics Madagascar, Tropical Asia Astripomoea 12 Tropical & S. Africa, Arabian Peninsula Ipomoea 635 Tropics & Subtropics Lepistemon 7 Tropical Africa, Tropical & Subtropical Asia to NE. Australia Lepistemonopsis 1 NE. & E. Tropical Africa Paralepistemon 2 S. DR Congo to KwaZulu-Natal Rivea 3 S. & SE. Asia Stictocardia 13 Tropical Africa, Tropical Asia & Pacific Turbina 20 Central and South America, South Africa

species-rich, which have been under the spotlight of the new molecular approaches. While some genera have been confirmed to be monophyletic, such as Convolvulus (with the integration of Calystegia ), Evolvulus or Operculina , others were resolved as nonmonophyletic, opening a new path of investigation for generic re-classification, for example for Ipomoea (Wilkin, 1999; Manos et al., 2001; Eserman et al., 2014; Muñoz-Rodríguez et al., 2019; Simões et al., 2022), Merremia s.l. (Stefanović et al., 2002; Simões et al., 2015), Seddera (Stefanović et al., 2002; Luna et al., 2013) and Bonamia (Stefanović et al., 2002; Simões et al., 2022).

Genera like Evolvulus , Hildebrandtia , Seddera , and Cladostigma have all been subjects of monographic treatments in earlier decades, but these studies predate the molecular phylogenetic approaches now available, such as Evolvulus (Van Ooststroom, 1934) , Hildebrandtia Vatke (Demissew, 1996) , Seddera

( Demissew & Mill, 2009) and Cladostigma Radlk. (Demissew, 1996) . For example, while Evolvulus was initially defined based on corolla shape and fruit dehiscence, recent studies suggest that molecular data may redefine its taxonomic boundaries,

especially in relation to closely related genera within the tribe. Similarly, Hildebrandtia and Seddera require molecular evidence to resolve their evolutionary relationships fully, especially considering recent studies that highlight polyphyletic lineages within the family ( Luna et al. 2012). Recent advances in molecular systematics have highlighted the need to reclassify polyphyletic genera within Convolvulaceae , such as Ipomoea and B onamia, which could significantly alter the number of recognised genera, particularly in the Eastern Hemisphere (Stefanović et al., 2003; Mitchell et al., 2016). For instance, the re-circumscription of the historically pantropical and polyphyletic genus Merremia s.l. has led to its division into four paleotropical genera — Merremia s.s., Camonea , Decalobanthus , and Xenostegia and one primarily neotropical genus, Distimake , which also includes substantial diversity in the Paleotropics ( Mitchell et al., 2016; Simões & Staples, 2017). Advances in molecular phylogenetics continue to provide critical insights that reinterpret morphological data, enabling more precise circumscription of genera and, as a general trend, an increase in generic richness, particularly in the Eastern Hemisphere(Williams et al., 2014).

Other integrative monographs include that of Convolvulus (Wood et al., 2015) and Operculina Silva Manso (Staples et al., 2020) . In addition to monographs, partial studies that either do not include molecular phylogenetic evidence, such as a synoptic revision of Decalobanthus Ooststr. , (Staples, 2022), or focus only on a regional subsection of the species of the genus, such as the African Neuropeltis Wall. ( Breteler, 2010) , the African Calycobolus Wild. ex Schult. ( Breteler, 2013) , the American Merremia ( O’Donell, 1941) or the South American Ipomoea (Wood et al., 2020) .

Generic monographs is an area where much work is still necessary in Convolvulaceae , as there are many gaps that still need to be filled in across the family, but, in many groups, this is pending taxonomic revision at tribal level, to help elucidate generic circumscription in the light of new molecular phylogenetic data, as many of the currently recognised genera are yet polyphyletic and needing to be re-circumscribed. Nonetheless, significant taxonomic progress continues to occur at species level, with many new species recently described, namely in Argyreia , Bonamia , Cuscuta , Distimake or Ipomoea ( Lawand & Shimpale, 2021) , as well as new combinations, e.g. in Distimake ( Petrongari et al., 2018) or Decalobanthus (Simões et al., 2020) or large scale nomenclature reviews, e.g. in Argyreia (Staples & Traiperm, 2017) . Thus, meanwhile, a lot of detailed species information is available also in floristic treatments (Table 3; Supplementary Material S1) and other geographically oriented publications, e.g. South American Ipomoea (Wood et al., 2020) , Ipomoea from Ghana (Williams et al., 2024) Convolvulaceae from Guinea ( Davis et al., 2024) or Convolvulaceae from Serra da Canastra ( Kojima et al., 2024), which are a good source of detailed, species-level information, for future revisionary studies.

One of the most challenging classification within Convolvulaceae is in the genus Ipomoea , the most species-rich genus in the family, encompassing 615 species (635 fide POWO, 2024; updated to 615 fide Simões et al., 2024). Phylogenetic studies have shown that Ipomoea is not monophyletic and that nine genera are nested within it (Wilkin et al., 1999; Manos et al., 2001; Eserman et al., 2014; Muñoz-Rodríguez et al., 2019; Simões et al., 2022). Furthermore, few of the proposed infrageneric subdivisions of Ipomoea are monophyletic when assessed with molecular data ( Miller et al., 1999; Manos et al., 2001; Stefanović et al., 2003). The reclassification of this large, widespread, incredibly variable genus remains a challenge, and efforts are ongoing to untangle it. A nomenclatural impediment to a re-classification of the group has recently been overcome ( Eserman et al., 2020; Applequist, 2023; Eserman et al., 2023; Wilson, 2024). Before the acceptance of this nomenclatural proposal, numerous name changes of many species would have been required if the large genus Ipomoea had been split into smaller genera, potentially destabilizing the nomenclature of Neotropical taxa. Now, it is possible to preserve the names of economically important species like sweet potato, as well as to maintain the important generic names such as Argyreia and Stictocardia , with far less nomenclatural disruptions for both Neotropical and Palaeotropical taxa (Simões et al. 2024).

One of the first major steps in the reclassification of the genus is the need for infrageneric monograph that clarify relationships and morphology across the genus. The most recent subgeneric classification proposed three subgenera: subgenus Eriospermum , subg. Ipomoea , and subg. Quamoclit ( Austin & Huáman, 1996), but none of these subgenera correspond to monophyletic lineages, highlighting the complex morphological diversity in this group. The relatively small Ipomoea subgenus Quamoclit (ca. 85 species) has received the greatest number of taxonomic treatments (e.g. O’Donell, 1959; Gunn, 1972; McDonald, 1987, 1995, 2001; Eserman, 2012). However, the rest of the infrageneric groups comprising ca. 550 species of Ipomoea have not yet been treated nor re-assessed in the light of molecular phylogenetic reconstruction and detailed assessments of morphology.

The reason for this vast difference between morphologically based taxonomy and evolutionary relationships reconstructed using molecular data is the rapid and convergent evolution of many morphological traits commonly used to circumscribe species and infrageneric groups. For example, a three-locular ovary is a commonly accepted synapomorphy of Ipomoea series Pharbitis ; however, another unrelated group, the newly described genus Muigaia , a l s o has a three-locularcapsule, despite other syanpomorphies unique across tribe Ipomoeeae , such as quadrangular stems, deeply dissected leaves and leaf-like stipules at the petiole insertion (Ngima et al., in press ). Furthermore, Pharbitis has also been described as having foliose sepals; this has also led taxonomists astray, leading some to interpret that some species of Distimake ( Meissner, 1869) or even Ipomoea pes-tigridis ( Hallier, 1893) , completely unrelated taxa, to be closely related to Pharbitis .

The fact that most infrageneric classifications and taxonomic treatments of Ipomoea have been geographically biased (e.g. focusing on tropical Americas, East Africa or Malesia) has created great confusion, especially given the broad geographical range and morphological variation of this genus, and render most of these classifications irrelevant until they can be carefully tested against integrated phylogenetic studies ( Austin & Huáman, 1996; Van Ooststroom 1953; Verdcourt 1963). As the availability of molecular data for tribe Ipomoeeae has seen exceptional progress in recent years(Wilkin et al., 1999; Manos et al.,2001; Eserman et al.,2014;Muñoz-Rodríguez et al., 2019; Simões et al., 2022), albeit with unbalanced sampling gaps for taxa from the Eastern Hemisphere which still needs to be overcome in the upcoming years, we are just starting to get a glimpse of the species-level relationships at a broader scale to be able to refine the boundaries of a monophyletic and morphologically diagnosable Ipomoea and establish, for the first time, a trans-geographic infrageneric classification for the genus, hand-in-hand with a comprehensive generic reclassification of the tribe Ipomoeeae . We are, after decades, or even centuries, of uncertainty and geographic biases, finally building up the necessary tools, global data, and a network of worldwide experts that could soon deliver a complete and global reclassification of this group at all scales: a sizeable challenge for the next years of taxonomic and systematic research in Convolvulaceae , both daunting and very exciting.

In the future, low coverage whole genome sequencing can be a promising approach to obtaining hundreds of genes, across all three genomes, for phylogenomic reconstruction. Genome sizes in Ipomoea are relatively small (2C = 1.5 to 5.2 pg) ( Ozias-Akins & Jarret, 1994), and with the recent release of the Illumina NovaSeq X , it is now more accessible and affordable than ever to sequence genomes at low coverage.

3.3. Ecology and Evolution

The reproductive biology and pollination ecology have been major areas of research in the ecology of the Convolvulaceae , particularly focused within the genus Ipomoea ( Baucom et al., 2011) . Evolutionary transitions from outcrossing to selfing in Ipomoea Table 3. Progress on Flora treatments for the family Convolvulaceae , organized by region or country. have been associated with independent reductions in floral traits, including corolla size, nectar and pollen production, herkogamy (the spatial separation of anthers and stigma), and other characteristics collectively known as the “selfing syndrome” (Sicard & Lenhard, 2011; Rosas-Guerrero et al., 2011; Rifkin et al., 2019; Liao et al., 2022). Such shifts increase reproductive assurance in environments with limited pollinator availability, but they are balanced by the potential negative consequences of inbreeding depression, which influences the diverse mating systems found in Ipomoea (Stucky, 1985; Díaz et al., 1996; Kowyama et al., 2000; Kaur et al., 2018; Delgado- Dávila & Martén-Rodríguez, 2021).

Continent Region/Country Year Genera Species

Africa Convolvulaceae of Guinea 2024 16 51 America Synopsis of the family Convolvulaceae in Mexico 2023 20 313 Oceania Flora of New Zealand 2023 7 29 Americas Flora of North America 2023 18 167 Asia Flora of Mongolia 2022 4 15 Africa Flora of Central Africa 2022 23 132 Americas Flora de Veracruz III 2021 1 10 Americas Flora do Brasil Online 2020 24 426 Americas Catalogue of the Vascular Plants of Chile 2018 7 36 Asia Flora of Cambodia, Laos and Vietnam 2018 22 108 Americas Vascular Plants of Cuba 2017 12 95 Africa Flore du Gabon 2015 9 31 Asia Flora of Peninsular Malaysia 2015 16 79 Americas Catalogue of the Vascular Plants of Bolivia 2014 17 186 Americas Convolvulaceae of Sonora, Mexico II 2012 1 21 Americas Convolvulaceae of Sonora, Mexico I 2012 9 84 Americas Flora of the West Indies 2012 15 144 Asia Co’s Digital Flora of the Philippines 2011 17 75 Asia Flora of Thailand 2010 24 119 Americas Manual de plantas de Costa Rica 2010 17 75 Americas Flora del bajío y regiones adyacentes II 2008 9 37 Americas Flora del bajío y regiones adyacentes I 2007 1 50 Africa Flora of Somalia 2006 18 58 Americas Flora Fanerogámica del Valle de México 2005 5 34 Americas Vines and Climbing Plants of Puerto Rico and the Virgin Islands 2005 11 45 Africa Flora of Southern Africa 2000 16 114 Africa Flora of Madagascar 2001 22 91 Americas Catalogue of the Vascular Plants of Ecuador 1999 19 152 Asia Flora of Taiwan 1998 14 44 Asia Flora of China 1995 20 129

Continent Region/Country Year Genera Species

Americas Flora de Veracruz II 1994 1 55 Americas Flora de Veracruz I 1993 11 85 Americas Catalogue of the Flowering Plants and Gymnosperms of Peru 1993 18 273 Oceania Manual of the Flowering Plants of Hawai’i 1990 13 32 Americas Flora of Panama 1987 14 158 Oceania Flore de la Nouvelle Calédonie 1984 7 13 Oceania Flora of Micronesia 1977 8 33 Asia A dictionary of Flowering Plants in India 1973 20 180 Americas Flora of Guatemala 1970 14 126 Asia Flora of the U.S.S.R 1969 5 64 Africa Flora of Tropical East Africa 1963 21 170 Asia Flora Malesiana 1953 21 198 Africa Flora of West Tropical Africa 1952 16 78 Americas Convolvuloideas de Uruguay 1959 7 26 Americas Convolvulaceas Argentinas 1959 12 86

Pollination studies on Ipomoea have predominantly emerged from North and Central America, where a wide array of pollinators including bees, butterflies, moths, and hummingbirds has been identified ( Bullock et al., 1987; Delgado-Dávila et al., 2016; De Santiago et al., 2019; Hassa et al., 2020). The varying contributions of these floral visitors to reproductive success of Ipomoea highlight the importance of assessing pollinator effectiveness in ecological studies of plant-pollinator interactions ( Araujo et al., 2018; De Santiago et al., 2019). The synchronisation of floral ephemerality, whether diurnal or nocturnal, plays a crucial role in shaping the temporal behaviour patterns of pollinators. ( Gimenes et al., 2021). Specifically, Ipomoea and Jacquemontia species are primarily visited by bees from the tribe Emphorini , which are solitary and oligolectic bees, collecting pollen from a restricted number of plant families, such as Convolvulaceae (Zanella, 2000; Pick & Schlindwein, 2011; Paz & Pigozzo, 2012, 2013; Paz et al., 2013; Santos et al., 2016; Paz et al., in prep.), Cucurbitaceae (Silveira et al., 2002) , and Malvaceae (Schlindwein & Martins, 2000; Schlindwein, 2004). These records suggest a closer relationship between these bees and the species within these families, indicating that the pollen flow facilitated by phylogenetically related bees, along with high floral fidelity, may promote behaviours that enhance pollination efficiency (De Santiago et al., 2019).

In addition to serving as foraging sources, the flowers of Ipomoea also act as sites for copulation and resting for the males of this tribe of bees, suggesting that they are essential for the maintenance of these pollinators in the region (Paz et al., 2013; Gomes et al., 2024). Despite extensive floral diversification aimed at attracting different pollinators, weak reproductive barriers have been found to permit the formation of fertile hybrids, highlighting the need for further research to clarify the roles of prezygotic and postzygotic isolation in speciation within the Convolvulaceae (Stucky, 1985; Díaz et al., 1996; Babiychuk et al., 2019). One mechanism identified as a potential benefit for selfing involves the close clustering of anthers around the stigma in some species, which not only facilitates high selfing rates but also protects against hybridisation through mechanical interference ( Ennos, 1981; Smith & Rausher, 2007; 2008a, b). The speciose parasitic genus Cuscuta presents a unique example of regressive evolution where the host-parasite flowering synchronisation in C. australis is observed. Here, the parasite detects the FLOWERING LOCUS T (FT) protein expressed by the host and optimises its flowering time by synchronisation of its physiology with that of the host (Shen et al., 2020). While Cuscuta consists of ~200 species, circumscribed into four subgenera, C. subg. Cuscuta , subg. Grammica , subg. Monogynella , subg. Pachystigma ), their reproductive biology and need for the maintenance of flowers or sexual reproduction has rarely been studied. This further illustrates that flowering phenology and reproductive fitness mechanisms remains understudied in this family.

Convolvulaceae serve as an ideal model for studying mechanisms underlying floral trait evolution, particularly due to its numerous transitions in pollination syndromes that result in convergent flower colours and morphology, although key traits like floral scent composition remain understudied (Streisfeld & Rausher, 2009; Des Marais & Rausher, 2010). While Ipomoea remains the most extensively studied genus in pollination ecology, research on other genera such as Calystegia , Argyreia , Operculina , Camonea Raf. , Evolvulus , Hewitti a Wight & Arn., and Merremia has revealed both the ecological diversity of the family and significant gaps in the current literature, especially in regions like Africa, Asia and Australia (Ushimaru & Kikuzawa, 1999; McMullen, 2009; Jirabanjongjit et al., 2021; Paul et al., 2023).

Ecological interactions related to seed dispersal among Convolvulaceae remain relatively unexplored, although effective dispersal strategies not only influence the colonisation of new habitats but also affect plant-pollinator interactions and the formation of complex plant communities. Morphological adaptations, such as the presence of lightweight and hairy seeds, favour dispersal by wind and water in various species of Ipomoea (Lakshminarayana et al., 2022) , as seen in the transoceanic dispersal of Ipomoea pes-caprae (L.) R.Br. ( Miryeganeh et al., 2014; Mircea et al., 2023) and Ipomoea violacea L. (Ridley, 1930; Alencar et al., 2021). In Cuscuta , the lightweight and small seeds are primarily dispersed by wind or water, facilitating colonisation in areas with abundant vegetation. This long distance seed dispersal is often due to endozoochory by waterbirds, rendering routine quarantine measures to be insufficient in regulating the colonisation of this parasitic plant in new habitats (Costea et al., 2016; Ho & Costea, 2018).

Herbivory and pathogen resistance in Convolvulaceae species, though less studied, are shaped by trade-offs that influence their ecological interactions and coevolutionary patterns. Research within this family indicates that resistance to herbivory is closely linked to pathogen resistance possessing genetic variations that confer quantitative resistance to both insect herbivores and natural pathogens like Colletotrichum dematium and Coleosporium ipomoeae , suggesting overlapping defence strategies (Simms & Rausher, 1993). Additionally, the trade-offs between resistance and tolerance strategies suggest that while resistance mechanisms can mitigate herbivore impacts, they may also limit plant tolerance to other stresses (Simms & Triplett, 1994). In Rivea ornata (Roxb.) Choisy , a rare species, florivory mainly affects non-essential floral structures, such as delicate corolla limbs, while sparing reproductive organs. The presence of latex-producing laticifers in Rivea suggests a specialised mechanism that deters florivores from consuming vital floral parts, thereby balancing pollinator attraction with defence. This adaptive strategy enables Rivea ornata to maintain high reproductive success despite florivory in this self-incompatible species, which relies entirely on pollinators for reproduction ( Chitchak et al., 2024). Nectar production in the extrafloral nectaries of some Convolvulaceae species—structures located at the base of the petiole, pedicel, or sepals—plays a significant role in plant defence ( Keeler, 1977; Paz et al., 2016a, b; Chitchak et al., 2022). These nectaries secrete nectar continuously throughout the day and year, attracting a variety of insects, particularly ants ( Beckmann & Stucky, 1981; Aguirre et al., 2013). The ants exhibit territorial and aggressive behaviours around these glands, thereby inhibiting or mitigating herbivory and florivory that could compromise floral attractiveness ( Keeler, 1980; Silva dos Santos Martins, 2018; Martins, 2020).

A key area of research within the Convolvulaceae focuses on plant-fungal interactions, particularly the symbiotic relationships between certain Ipomoea species and clavicipitaceous fungi, such as Periglandula ( Cook et al., 2019; Beaulieu et al., 2021). Around 450 species within the family are estimated to engage in symbioses with

Periglandula , which produces ergot alkaloids that are vertically transmitted through seeds. These alkaloids provide critical protection against herbivores and pathogens, highlighting their role in the plant’s defence mechanisms. Other alkaloids, such as swainsonine produced by fungi in the order Chaetothyriales , and terpenoid indole alkaloids synthesised by the plants themselves, have also been identified as essential defence compounds ( Cook et al., 2019). However, research into the diversity of alkaloid-producing fungi and their interactions with Periglandula within the Convolvulaceae is still ongoing. Further studies are needed to fully understand the diversity, distribution, and ecological function of these compounds in this plant family.

The ecology of parasitism in the Convolvulaceae reveals a fascinating evolutionary history in Cuscuta , the only parasitic genus in this family. A key evolutionary adaptation in parasitic plants like Cuscuta is the development of the haustorium, a specialised organ that connects the parasite to its host’s vascular system, enabling the transfer of water, nutrients, and even genetic material between the two plants (Yoshida et al., 2016; Fig. 2g). Phylogenetic studies suggest that Cuscuta diverged from non- parasitic relatives, with accelerated genome evolution, particularly in terms of gene loss related to photosynthesis, a trait rendered unnecessary by its parasitic nature. Genome reduction has been a hallmark of Cuscuta evolution, particularly in terms of plastid gene loss across clades where gene loss reflects the loss of photosynthesis and total reliance on host plants ( Braukmann et al., 2013; Sun et al., 2018). The parasitic lifestyle of Cuscuta allows it to exploit diverse ecological niches by parasitising a wide range of host plants, including other parasitic plants, affecting the dynamics of plant communities and ecosystems (Stefanović & Olmstead, 2005; Piwowarczyk et al., 2017; Costea et al., 2021).

The ability of Convolvulaceae to adapt to disturbed environments, such as regions with low nutrient availability and high sunlight exposure, is remarkable. This resistance to adverse conditions, combined with rapid life cycles, facilitates the proliferation of various species in agricultural fields.In these environments, species of Ipomoea and Distimake are often considered weeds that compete with soybean, corn, cotton, and sugarcane crops for resources (e.g. Azania et al.,2009; Labonia et al.,2009; Lucio et al., 2011; Chauhan et al., 2012; van Etten et al., 2016; Paul et al., 2023). Some species too are adapted to saline soils, such as I. pes-caprae , which thrives in coastal dunes and mangrove areas, where salinity tolerance is crucial for survival ( Miryeganeh et al., 2014; Mircea et al., 2023). Moreover, although these flowers are visited by a diversity of animals, they constitute an important resource for the maintenance of local pollinators, especially in human disturbed and urban environments.

3.4The genomic leap: new data and rapid advances Convolvulaceae has seen a significant increase in genomic resources in recent years. In terms of nuclear genomes, there are 3distinct Ipomoea species ( I. batatas , I. trifida (Kunth) G. Don , and I. triloba L.) and one Cuscuta species ( C. australis R. Br. ) with sequenced and annotated genomes. Additionally, a draft genome for the Japanese morning glory ( I. nil ) has been released. As for organellar genomes, numerous chloroplast genomes (43) have been sequenced across the family, providing insights into plastome evolution, structural variations, and gene loss associated with the parasitic lifestyle in Cuscuta . Mitochondrial genomes have also been characterised for 17 species, revealing complex structures and potential implications for cytoplasmic male sterility. These genomic resources are key for understanding the evolution and biology of Convolvulaceae , and they will facilitate future research and breeding efforts aimed at improving sweet potato and other species in this family (Supplementary Materials S2, S3).

The most recent phylogenetic study of Convolvulaceae relied on Angiosperms353, with very positive results, and resolving intricate relationships not successfully resolved before, such as the non-monophyly of tribe Merremieae , and the close relationships of Distimake with the clade that includes tribe Ipomoeeae (Simões et al., 2022) . However, many systematic studies of Convolvulaceae still rely on Sanger sequencing (single gene) studies, as they are less costly than the most advanced genomic techniques. In Convolvulaceae , the largest family phylogenetic study which led to the most recent tribal level classification of the family (Stefanović et al., 2002, 2003), used only chloroplast markers: rbcL, trnL-F, atpB, and matK. The initial purpose of the study was to establish the position of Cuscuta within the family and, although not successful at this point, it provided an important framework for further systematic studies of the family. A reclassification of tribe Merremieae used both nuclear ( ITS) and chloroplast markers ( trnL-F, matK and rps16), and other molecular systematic studies have tried to follow the same choice of markers, to allow consistency and complementarity of the datasets, as has been done with success in recent studies in Argyreia (Rattanakrakang et al., 2022) .

Thus, genetic studies in Convolvulaceae come with a degree of challenge, e.g. for DNA extraction, due to the high quantity of phenols. While not all projects seem to find the same level of difficulty, it is not uncommon for researchers to find it challenging to successfully sequence some genetic regions, particularly the longer genes, and most commonly this derives from issues with the DNA extraction, where there is sufficient DNA yield to continue to the sequencing steps, but it is not clean enough, or has high concentration of particular metabolites which interfere with the success of the PCR. The cleaning step of the DNA extraction is of the utmost importance in Convolvulaceae and should be optimised to deal with the presence of phenols, or sugars. Also, there is an abundance of non-coloured or milky sap in some species causing the sticky supernatants during the extraction. A protocol for DNA extraction and single gene markers (primers and PCR conditions) is here proposed (Supplementary Materials S4, S5), to help with the implementation of these techniques in studies involving Convolvulaceae , which could be optimized depending on available reagents or tailored to the taxonomic group being targeted if necessary

3.5 Palynology

As discussed earlier, molecular systematic studies of Convolvulaceae have repeatedly confirmed the value of micromorphological characters for predicting relationships, identify inconspicuous synapomorphies for natural groups, and circumscribe - or correctly place – species, genera, tribes and subfamilies.

Pollen, as an example, has been of extreme importanceinsystematicstudiesofConvolvulaceae, starting with the earliest classification of Hallier, which predicted the division of the family into two major groups: 1) Echinoconieae, having spiny surfaced pollen grains and 2) Psiloconieae, having psilate (non-spiny) pollen grains ( Hallier, 1893). Molecular phylogenetic studies have demonstrated that the echinate (spiny) pollen evolved a single time in the family, for which the informal group “Echinoconieae” is monophyletic. However, the remainder of the family possesses almost completely smooth pollen, or bearing micro-spines, and constitutes a paraphyletic group. Echinoconieae currently correspond to tribe Ipomoeeae , and the spiny pollen is a synapomorphic trait for this tribe.

Palynological studies in the tribe Ipomoeeae have consistently reported the unique appearance of spiny pollen, distinguishing this tribe from the others in the family ( Hallier, 1893; Sengupta, 1966; Hsiao & Kuoh, 1995; Traiperm, 2002; Tellería & Daners, 2003; Rajurkar et al., 2011; Saensouk & Saensouk, 2018). The pantoporate-type aperture with spines or spinulate processes is applied as a key character of structure and sculpture on pollen in Ipomoeeae . There are two main subtypes of pollen microstructures based on the exine stratification, namely the presence and absence of extraporal regions ( Hsiao & Kuoh, 1995). The pollen including tetragonal to hexagonal areas with extraporal regions is likely to be found in the genera Ipomoea , Lepistemon and Lepistemonopsis (Sengupta, 1966; Hsiao & Kuoh, 1995; Tellería & Daners, 2003; Rajurkar et al., 2011; Saensouk & Saensouk, 2018). The pollen features without the extraporal region are found in Argyreia and most Ipomoea from the Old World ( Hsiao & Kuoh, 1995; Traiperm, 2002; Tellería & Daners, 2003; Saensouk & Saensouk, 2018), which could suggest a palynological synapomorphy for subtribe Argyreineae . Various qualitative and quantitative characters on the two subtypes of pollen were also observed that could help palynologically characterise the genera or subtribes within tribe Ipomoeeae , with possible systematic value as synapomorphies for the clades or genera. Pollen of the remaining genera in Ipomoeeae is awaiting to be better studied in order to fully understand the evolutionary relationships among genera and taxa in this tribe, and contribute to a successful generic re-circumscription of this group.

Erdtman (1952) suggested that Convolvulaceae are an eurypalynous family, and that its taxa could be grouped into ‘ Ipomoea type’ and other types. Based on the pollen morphology, the evolutionary trends were also predicted by various studies (Wodehouse, 1935; Sengupta, 1972). Scanning Electron Microscope (SEM) studies were conducted by Kattee et al. (2016), who examined 34 species of Convolvulaceaebelongingto five genera and studied exine pattern in the Indian Convolvulaceae . Saensouk and Saensouk (2018) studied morphology of pollen grains of 45 taxa belonging to seven genera from Thailand and pointed out that pollens from the Thai Convolvulaceae can be divided into six pollen types based on their aperture viz., Polypantoporate, Hexacolpate, Tricolpate, Periporate, Pantoporate and Zonocolpate ( Fig.1).

Studies in the non-spiny members of the family have, thus, revealed important micromorphological with taxonomic value, such as the number and distribution of apertures, and shape and size of the micro-spines on the surface, supporting genera or morphological groups within the genera, for example Bonamia (Moreira et al., 2019) , Cuscuta (Welsh et al., 2010) , Decalobanthus (Simões et al., 2021) , Jacquemontia ( Buril et al., 2014) , Operculina (Simões et al., 2019) and Xenostegia ( De Man & Simões, 2021) .In general, pollen characters have shown to be of high predictive value, for example to determine species assignment to a given genus/subgenus which has proven to be supported by molecular phylogenetics (Ferguson et al., 1977; Sosef et al., 2019). Exceptionally, cases of evolutionary convergence have been reported, for example in Distimake Vitifolius (Burm.f.) Pisuttimarn & Petrongari , a species which presented 6-zono- colpate pollen type that was considered diagnostic of genus Camonea , and therefore the species was transferred to this genus (as Camonea vitifolia (Burm.f.) A.R.Simões & Staples ) which later, more robust, molecular phylogenetic studies proved not be the case, but belonging in Distimake instead, where such pollen type was not yet documented (Pisuttimarn et al., 2023). Such cases are rare in Convolvulaceae , where pollen most commonly has high systematic predictive value, but it needs to be considered that such value of palynological characters should be continuously evaluated in an evolutionary framework.

3.6 Anatomy

Anatomically, Convolvulaceae are also one of the families that are best characterised. As overall features, the presence of two vascular variants, the intraxylary phloem ( Fig. 2 a-c) and the successive cambia ( Fig. 3a) make it unique in the angiosperms. Another conspicuous feature is the presence of laticifers ( Fig. 2b, d), which are articulated, nonanastomosing (Fahn 1979; Carlquist & Hanson 1991; Ceja-Romero & Pérez-Olveda, 2010), producing a white or yellowish exudate. These laticifers are present in the cortex, pith ( Fig. 2b), secondary phloem ( Fig. 2d), and conjunctive tissue. In the secondary xylem, vessels may be solitary or in multiples ( Fig. 2a, c-e, H), being either radial or tangential multiples ( Fig. 2a, c-e, h). Tyloses are very common in the vessels, and they may be either regular ( Fig. 2d, h) or sclerotic ( Fig. 2e). Another extremely common feature is the presence of the entire gradation of imperforate tracheary elements, i.e., true fibres, fibre-tracheids, and true tracheids ( sensu Carlquist, 2001; Olson, 2023; Fig. 2f), commonly co-occurring ( Carlquist & Hanson, 1991). Axial parenchyma is typically paratracheal, vasicentric to aliform ( Fig. 3c, e), with or without short confluences, commonly also in patches, the latter non-lignified ( Fig. 2h). Rays of two different sizes are typically present in the lianas, the uniseriate, short rays and the wide, multiseriate rays ( Fig. 2i). The uniseriate rays are lignified ( Fig. 2f, i), while the wide rays are non-lignified ( Fig. 2i). The latter connects to the conjunctive tissue, interconnecting the different successive cambia ( Fig. 2a). Non-lignified parenchyma is very common in the species with successive cambia ( Fig. 2a, h). Sometimes the entire stem and root fissures due to parenchyma proliferation ( Carlquist & Hanson, 1991). Druse crystals are present both in axial ( Fig. 2h) and ray parenchyma, sometimes also within the tyloses ( Carlquist & Hanson, 1991). Amiloplasts are extremely common in all parenchymatic tissues (Cejas-Romero & Pérez-Olveda, 2010), both in tissues of primary and secondary origin ( Fig. 2b). The secondary phloem has sieve tubes solitary or in radial rows ( Fig. 2d), sieve plates simple to compound, and in most species the phloem is devoid of sclerenchyma ( Fig. 2d), although clusters of sclereids sometimes are formed in the nonconducting phloem. Below we give additional information on the vascular variants that are so conspicuous to the family.

Intraxylary phloem ( Fig. 2 b-c) is probably the most commented shared anatomical feature of the Convolvulaceae , and it has been used to support their relationship to the Solanaceae (Schenck, 1893; Solereder, 1908; Metcalfe & Chalk, 1950; Stevens, 2001 onwards). If indeed intraxylary phloem is a synapomorphy of the clade [ Convolvulaceae , Solanaceae ], its absence in Humbertia , Cuscuta ( Fig. 2g) and a few members of Convolvulus (e.g., Convolvulus floridus L.f. from the Canary Islands, pers. obs.) represents independent loses. The intraxylary phloem in Convolvulaceae is derived from bicollateral vascular bundles ( Metcalfe & Chalk, 1950). However, it is very common that during development, an internal vascular cambium is formed between the protoxylem and the primary intraxylary phloem, giving rise to secondary phloem towards the centre of the pith ( Fig. 2c) and secondary xylem towards the protoxylem, obliterating the entire pith ( Carlquist & Hanson, 1991; Rajput et al., 2008, 2013; Patil et al., 2009; Rajput & Gondaliya, 2017). Sometimes these secondary growth increments are termed inversed vascular bundles, but this is a misnomer, since the term vascular bundle should be used exclusively to primary structure. Successive cambia have been recorded in more than 10 genera of the family ( Argyreia , Calonyction Choisy,

Convolvulus , Dicranostyles , Distimake , Erycibe , Hewittia , Ipomoea , Maripa , Merremia , Porana Burm. f. and Rivea ; Metcalfe& Chalk, 1950, Carlquist,2001); however, some of these previously cited genera have been merged into Ipomoea (e.g., Calonyction and Rivea ). Successive cambia are originated in the outer limits of the vascular cylinder, in the pericycle (Terrazas et al., 2011), which corresponds to the master cambium of Carlquist ( Carlquist, 2007). The pericycle divides in many rows forming a parenchymatic band of variable thicknesses. Within this band, a new cambium is formed. This new cambium starts producing secondary xylem and phloem, enclosing parts of this previously proliferated parenchyma, which will now be recognised as conjunctive tissue. The conjunctive tissue, being parenchymatous and nonlignified, connect successive cambia and may give rise to yet new cambia at later stages. These new cambia can develop with either regular or opposite orientations, in the latter producing xylem to the outside of the stem and phloem to the inside (Rajput et al., 2008, 2013). A broad scale anatomical studies of the entire Convolvulaceae is needed to understand when the successive cambia appeared in the family and how they diversified. In the genera where they are present, they are present in lianas, shrubs, and trees (e.g., Ipomoea series Arborescentes ; McDonald, 1992; Ceja-Romero & Pérez-Olvera, 2010; Terrazas et al., 2011). In trees of the Ipomoea series Arborescentes , the number of successive cambia goes much beyond that of lianas ( Carlquist & Hanson, 1991), while in the commonly cultivated shrub Ipomoea carnea , new cambia appear only in very advanced phases of secondary growth, sometimes even being recorded as absent ( McDonald, 1992). Successive cambia are thought to increase the flexibility in climbers, while in the Ipomoea series Arborescentes they may act as a storage tissue ( pers. obs.) similarly to what suggested for the roots ( Artschwager, 1924). The successive cambia of roots cause complete breakdown of the secondary tissues ( Fig. 3a), by forming concentric cambial islands which produce a few xylem vessels inwards and phloem parenchyma outwards ( Fig. 3b), with an enormous amount of amiloplasts ( Fig. 3b; Artschwager, 1924). Regarding the leaves, the main veins have typically bicollateral vascular bundles ( Fig. 3 c-e), with or without a fibrous cap ( Fig. 3 c-d). The paradermal section of the leaf epidermis shows cells walls can be straight or curved (Solereder, 1908) or sinuated in Argyreia (Traiperm et al., 2017) . The blades display a single epidermal layer to both sides. ( Fig. 3 c-d). Tanniniferous epidermal cells are common in the adaxial epidermis (Solereder, 1908; Ketjarun et al., 2016; Fig. 3 f-g). The mesophyll is heterogeneous, dorsiventral (the most common; Fig. 3f) or isobilateral (dominant in genera like Convolvulus , Evolvulus , Cressa ; Metcalfe & Chalk, 1950; Fig. 3g). In the dorsiventral mesophyll it is common to find a palisade parenchyma and spongy parenchyma ( Fig. 3f), but sometimes the spongy parenchyma is poorly developed to isobilateral (e.g., I. pes-caprae ; Fig. 3g), and palisade and spongy cells are different in shape. The vascular bundles on the mesophyll are either collateral ( Fig. 3 f-g) or bicollateral. Laticifers can be present in the cortex of the main veins and throughout the mesophyll, commonly associated to the vasculature ( Fig. 3 fg). The presence of crystalliferous idioblasts with druses of different forms and sizes is widespread

(Solereder, 1908; Fig. 3g).