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 : 268-271

Why study Convolvulaceae ?

2.1 Economic importance and traditional uses

Convolvulaceae are an economically significant plant family, with a range of economic and traditional uses including ornamental, food, medicinal and recreational drugs. One of such key species is the crop sweet potato ( Ipomoea batatas (L.) Lam.), a staple in the human diet, with a global trade value of USD 744 million as of 2022 (The Observatory of Economic Complexity, https:// oec.world). Its high nutritional content, including essential vitamins, minerals, and dietary fibre, combined with its resilience to drought, makes it

Table 1. Diagnostic characters for subfamilies of Convolvulaceae .

Subfamily Style shape Stigma Stigma

Cuscutoideae 1 or 2 2 Globose to ellipsoid Humbertioideae 1 1 Capitate Eryciboideae 0 (much compressed) 1 Disc (flattened) Cardiochlamydeae 1 1 Globose Dichondroideae * 2 2 or 4 Globose, club-shaped or filiform Convolvuloideae 1 2 Globose, club-shaped or filiform

a crucial component for food security strategies, being an adaptable crop across a diversity of climates ( Alam, 2021). Beyond its role as a staple food, sweet potato offers potential health benefits. It is a nutrient-dense, low-glycaemic option that supports balanced blood glucose levels. Sweet potatoes are also rich in anthocyanins, including peonidin and cyanidin derivatives, which exhibit antioxidant and anti-inflammatory properties, potentially surpassing other vegetables due to their free radical scavenging abilities. These compounds may help mitigate oxidative stress, a factor linked to chronic conditions such as cardiovascular disease and diabetes (Willcox et al., 2009; Li et al., 2019).

Other species in Convolvulaceae are known for their enlarged storage roots, which often serve as survival food during times of scarcity (e.g. Ipomoea capillacea (Kunth) G. Don ; I. jicama Brandegee , from Tropical America, and I. longituba Hallier f. in East Africa) (Urbina, 1906; Kabuye, 1986; Sandoval-Ortega et al., 2023). There are also some species in the Northeast of Brazil which roots are collected from the wild for human consumption: these are popularlyknown as“batata-da-serra”or“batatinhada-serra”, and despite the name (“batata” meaning “potato”), the taste is similar to pear. These species were found being marketed locally before they were recognised by science, i.e. Ipomoea pintoi O’Donell , I. ana-mariae L.V. Vasconcelos & Sim-Bianch. , and I. serrana Sim-Bianch. & L.V. Vasconcelos , and they are rare,despite being explored as a food source (Vasconcelos et al., 2016).

Another economically significant species in the family is Ipomoea aquatica Forssk. , commonly grown as a vegetable for its edible leaves and stems, and particularly popular in Asia, known as ‘water spinach (English), ‘kankong’ (Malay) or ‘pak bung’ (Thai). Its leaves are rich in dietary fibres and glycosides, which have also been associated with hypoglycaemic and antioxidant properties ( Hamid et al., 2011). Ipomoea aquatica has been utilised in southern Asia since at least A.D. 300, and possibly as early as 200 B.C. People have traditionally gathered this plant from the wild and cultivated it for its nutritional and medicinal value. When Europeans arrived in southern Asia during the late 1400s, they recognised its benefits and contributed to its dissemination worldwide ( Austin, 2007).

Beyond dietary uses, Convolvulaceae include species with medicinal, cultural, and other practical applications. Medicinally, the roots of Ipomoea purga (Wender.) Hayne have been cultivated in Mexico for centuries for their purgative properties, forming part of a traditional production system that supports local economies (Urbina, 1906; Linajes et al., 1994). Ipomoea stans Cav. , also from Mexico, and commonly known as ‘tumbavaqueros’, has shown anxiolytic, sedative, and anticonvulsant properties, supporting its traditional use for nervous disorders and seizures ( Díaz, 1976; Herrera-Ruíz et al., 2007). Likewise, Bonamia ferruginea (Choisy) Hallier f. (‘cipó-tuíra’) is traditionally used in Brazil to treat jaundice, hepatitis, and malaria (Rodrigues, 2006; Paes & MendonÇa, 2008). Furthermore, Ipomoea mauritiana Jacq. has been extensively investigated for its potential inclusion in herbal formulations due to its antihypertensive, fibrinolytic, and antioxidant activities ( Chandira & Jayakar, 2010; Jain et al., 2011). Ipomoea mauritiana is often miscited in the literature as Ipomoea digitata (L.) L., a West Indian endemic that does not occur in Asia (Rhui-Sheng & Staples, 1995; POWO, 2024).

This family also includes plants with cultural significance, such as Turbina corymbosa (L.) Roth (syn. Rivea corymbosa (L.) Hallier f.), which has been used in ritual contexts by Mesoamerican civilisations and their descendants for its psychoactive effects, attributed to ergot alkaloids with similar effects to the psychedelic drug LSD [Lysergic acid diethylamide] (Schultes& Hofmann, 1973). The production of these compounds with hallucinogenic effects have been established to derive from a plant-fungal symbiosis, of which Convolvulaceae are a rare example among flowering plants ( Panaccione et al., 2005; Schardl et al., 2007; Beaulieu et al., 2013; Florea et al., 2017; Steiner and Leistner, 2018; Cook et al., 2019; Olaranont et al., 2024). Additionally, Ipomoea caudata Fernald has been historically used in hunting, with its crushed roots employed as a fish poison to facilitate capture (Urbina, 1906).

Despite these known applications, many species within this family remain understudied, offering significant potential for future exploration. More detailed information on chemical compounds found in Convolvulaceae , their potential use and pharmaceutical properties can be found in the handbook “ Solanaceae and Convolvulaceae : Secondary Metabolites:

Biosynthesis, Chemotaxonomy, Biological and Economic Significance (A Handbook)” ( Eich, 2008). Examples of further uses can be found in Supplementary Materials (S6, S7). Convolvulaceae also have important ornamental value: with floral shapes ranging from funnel-form to bellshaped and an impressive array of colours, many species are highly prized as ornamental plants. These species are celebrated globally, known as ‘liserons’ in French, ‘morning glories’ ( Ipomoea ) or ‘bindweeds’ ( Convolvulus or Calystegia R.Br. ) in English, ‘campanillas’ in Spanish, and ‘asagao’ in Japanese, of which Ipomoea nil (L.) Roth) and I. indica (Burm.) Merr. are among the most popular cultivated species.In Japan, the asagao hold a special place in culture, highlighted by the Iriya Asagao Matsuri, an annual festival in Tokyo that attracts morning glory fans, from July 6–8 (https://www. gotokyo.org/en/spot/ ev054/index.html). While many species are appreciated for their large, showy, flowers, others are appreciated for their decorative fruits ( Distimake tuberosus (L.) A.R. Simões & Staples, or ‘woodrose’), ornamental seeds ( Merremia discoidesperma (Donn. Sm.) O’Donell , or “Mary beans”), or attractive foliage, such as Dichondra repens J.R. Forst. & G. Forst. Some species, like Dinetus racemosus (Roxb.) Sweet (syn. Porana racemosa Roxb. ), are valued for their whiteflowered, dripping, paniculate inflorescences, while compact shrubs like Evolvulus nummularius (L.) L. display charming small blue flowers covering the ground. These aesthetic qualities, coupled with their role in supporting pollinators, make Convolvulaceae essential in horticulture and in efforts to conserve biodiversity and promote ecological research.

2.2 Species richness and untapped diversity With Convolvulaceae comprising 1,955 species, subfamily Convolvuloideae is, by far, the largest and most taxonomically diverse of all the six subfamilies, including 1,198 species (61% of the species of Convolvulaceae ) and 24 genera (42% of the genera of the family); it is also the subfamily that includes some of the most economically important species, such as the crops “sweet potato” ( Ipomoea batatas L.) and “water spinach” ( Ipomoea aquatica Forssk. ), the ornamental “morning glories” ( Ipomoea spp. ), and “bindweeds” ( Convolvulus spp. and Calystegia spp. ) (POWO, 2024, Table 1). At generic level, the species diversity is, also, very unevenly distributed. The greatest species richness is concentrated in three largest genera: Ipomoea (615 spp.), Cuscuta L. (220 spp.) and Convolvulus (203 spp.), which together contain 54% of the total number of species of the family.Other significantly diverse genera are Argyreia (143 spp.), Jacquemontia (106 spp.), Evolvulus (106 spp.), Erycibe (73 spp.) and Bonamia Thouars (70 spp.). Yet, more than half of the genera of Convolvulaceae (35 of the 57 genera) contain fewer than 10 species. Of these, a handful are likely to be soon submerged into other genera, for lack of phylogenetic support and morphological diagnosability, as was recently the case of Blinkworthia Choisy (Rattanakrajang et al., 2018; Rattanakrajang et al., 2022). However, many of these smaller, in some cases monotypic, genera represent distinct evolutionary lineages, morphologically clearly distinct and geographically restricted, such as the genera endemic to Madagascar ( Cardiochlamys Oliv. , Humbertia Lam. , Rapona Baill. ), Australia ( Duperreya Gaudich , Wilsonia R. Br. ) or Brazil ( Daustinia Buril & A.R. Simões ). Beside intrinsic biological and evolutionary reasons, it may also be that the most economically important genera (e.g. Ipomoea , Convolvulus ) have historically received more attention and have, as consequence, seen more species described at a faster pace. Since 2000, 295 new species of Convolvulaceae have been described across 21 genera, of which 50% in Ipomoea alone, followed by Cuscuta (8%), Convolvulus (7%), Jacquemontia (7%), Argyreia (6%) and Bonamia (6%) (https://ipni.org, accessed Dec. 2024). More recent studies targeting smaller, less studied genera, such as Evolvulus , Dicranostyles , Distimake , Erycibe , Maripa or Xenostegia have demonstrated that there is still much undocumented diversity, with new species still being described (Silva et al., 2014; Moreira et al., 2021; Belo et al., 2023; Santos et al., 2023; Pastore et al., 2023, 2024; Patil et al., in press ). More strikingly, in 36 of the 57 currently accepted genera of Convolvulaceae , not a single new species has been described in the past 24 years (since 2000). It is possible that the species-level diversity of the family has been significantly underestimated and could increase if more taxonomic studies were conducted on these overlooked genera, with targeted field collections and careful examination of herbarium collections.

2.3 Centres of diversity and endemism Convolvulaceae are primarily found in tropical and subtropical regions, which house 52 of the 57 genera. The remaining five genera occur in temperate regions, of which two — Calystegia and Polymeria R.Br. — occur exclusively in temperate biomes ( Mitchell et al., 2016). Convolvulus , the largest genus in the tribe Convolvuleae , is widespread across temperate zones, exhibiting notable diversity in the Mediterranean, Western Asia, and the Southern Hemisphere temperate regions, such as southern Africa, Australasia, and South America (Wood et al., 2015; Mitchell et al., 2016). The Eastern Hemisphere (Paleotropics, or Old World) is an important centre of generic diversity for Convolvulaceae , hosting 77% of the family’s generic richness (44 of the 57 genera), with 18 genera restricted to this region. The Western Hemisphere (primarily tropical Americas) houses 22 genera, half the diversity observed in the Eastern Hemisphere and fewer than the diversity of Madagascar alone, where 23 genera occur, including five endemic genera ( Mitchell et al., 2016). The African mainland supports 30 genera, of which nine are endemic, while Australasia and the Pacific contain 36 genera, with 11 regionally restricted. Similarly, tropical Asia and Malesia comprise 33 genera, including eight endemic genera, whereas Australia and Oceania harbour 19 genera, of which three are endemic (POWO, 2024).