Sabdariffa
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publication ID |
https://doi.org/10.1071/SB24013 |
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persistent identifier |
https://treatment.plazi.org/id/03AC0268-C370-D55B-FC82-F9049DF4FEC7 |
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treatment provided by |
Felipe |
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scientific name |
Sabdariffa |
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General biogeography and diversity of Sabdariffa
Sabdariffa is pantropical in extent though most species are tropical, occurring in the Americas, Pacific, Australia, Asia and Africa. Hotspots of species diversity in Sabdariffa can be identified in tropical America (especially Brazil), northern Australia and tropical Africa. The greatest proportion of species found in each of these areas constitute localised endemic species and few have naturally broad distributions. For example, most locally endemic species in northern Australia are almost entirely associated with rocky outcrop substrates, especially sandstone ( Craven et al. 2003). This suggests that drivers of speciation in northern Australia may be largely edaphic and associated with the natural isolation of the rocky areas in which the species occur. Hybridisation between members of Hibisceae is usually restricted to related species ( Janakiram and Patil 2017). However, breeding barriers are clearly present as the co-occurrence of multiple species is not particularly unusual in some regions (Satya 2012; Satya et al. 2012, 2013 a, 2013 b). Many Australian species of Sabdariffa appear to have allopatric ranges, i.e. for the most part, these are geographically isolated from each other’s presumed closest relatives and co-occurring species are commonly less closely related ( Craven et al. 2003; R. L. Barrett and M. D. Barrett, pers. obs.). More closely related species may still possibly hybridise if the distributions happen to overlap (see Wilson 1994) and therefore individual collections with anomalous morphology should be carefully considered to determine if these may be hybrids. Several such anomalous specimens await further assessment.
One notable exception to these patterns of local endemism is currently presumed to be Sabdariffa diversifolia (Jacq.) McLay & R.L.Barrett that has a very broad distribution across Africa (including Madagascar), Asia, to Australia, New Zealand, the Pacific and Central and South America. Although the native range has occasionally been debated (e.g. Gardner 1985; Sykes 1988), fossil pollen records that pre-date human occupation have been found in both New Zealand and the Galápagos, clearly demonstrating the broad natural occurrence in the region ( Newnham and Lowe 1991; van Leeuwen et al. 2008 ). Te Reo Māori names for this species (Aute-Purarangi and Purarangi) are on record from the early 1800s (P. de Lange, pers. comm.). There is also a distinctive morphotype that is restricted to ultramafics at Surville Cliffs in the far north of New Zealand ( de Lange et al. 2018). We note that pollen core evidence suggests an introduction to Norfolk Island by Polynesian settlers ( Macphail et al. 2001), therefore each case of dispersal should be considered independently. Consideration should perhaps be given to whether this wetland species is able to be ocean-dispersed, as in Talipariti ( Yamazaki et al. 2023) or whether the habitat lends itself to associated dispersal by waterbirds. The appearance of a population in a petrel colony on an isolated oceanic rock stack 300 km south of other known occurrences in New Zealand lends weight to some form of facilitated dispersal by these skim-feeding birds (P. de Lange, pers. comm.).
Roselle and kenaf are currently also very widely distributed throughout the global tropics. The wild origins of these species are inferred to be tropical Africa ( Wilson 1994; Satya et al. 2013 a, 2013 b; Hendy 2019) whereas all other occurrences around the world can be inferred by human-mediated dispersal ( Alexopoulou et al. 2013; Satya et al. 2013 a, 2014). Considerable morphological diversity exists within the native ranges of both roselle and kenaf and numerous morphotypes have been utilised (e.g. Howard and Howard 1911; Fig. 2 View Fig , 3 View Fig ). Although only a single morphotype is usually found in a given area of introduction, several morphotypes have been identified among introduced populations.
Speciation within section Furcaria has at least in part also been driven by chromosomal rearrangement, in particular polyploidy. Our knowledge in this area is largely due to the work of Margaret Menzel (1924–1987), who undertook investigations spanning a great deal of her lifetime. Extraordinary chromosomal diversity has been documented in the genus ( Menzel and Wilson 1961, 1963, 1966, 1969; Menzel 1963, 1986; Wilson and Menzel 1964; Menzel and Martin 1970, 1971, 1974, 1980; Martin and Menzel 1971, 1972; Kachecheba 1972; Fernández 1974; Dasgupta and Bhatt 1981; Menzel and Hancock 1984; Menzel et al. 1983 a, 1983 b, 1986; Fryxell and Stelly 1993; Fernández et al. 2003) and chromosome numbers are known in a large proportion of species in the genus. Thirteen distinct genome groups have been identified that are largely associated with specific biogeographic regions (e.g. 9 of the 13 genome groups occur in sub-Saharan Africa) but some genome groups are shared across continents in various combinations ( Wilson 1994, 2006). The complex genome origins provide significant challenges for reconstructing nuclear genomes and analysis of nuclear data due to paralogy, though there is a growing number of chloroplast genomes that have been published for Sabdariffa and related Hibisceae ( Xu et al. 2019; Abdullah et al. 2020; Zhang et al. 2020; Eriksson et al. 2021; Wang ZQ et al. 2022; Kwon et al. 2022, 2023, 2024; Koo et al. 2023; Go et al. 2024). Population-level studies in other Hibisceae genera provide models for future studies on Sabdariffa ( Yamazaki et al. 2023; Mashburn 2024).
These data offer some insight into areas of origin for some species, and patterns and processes of speciation within Sabdariffa . However, as noted above, a species-level phylogeny of the genus remains lacking and timing of diversification is unknown. This group will likely prove to be very interesting for exploring the timing and pattern of dispersal around the global tropics, and mechanisms of chromosomal evolution.
Ecology
Although species in Sabdariffa are perennial, most are shortlived (5–10 years), disturbance-following species. A few species can form small trees and the average age expectancy may be more in the order of 20–30 years. These longer-lived species are still considered to be disturbance followers, only with longer lifespans enabled by wetter environments ( Craven et al. 2016).
As with many Malvaceae , seeds of Sabdariffa species are commonly long-dormant (likely in the order of 10–50 years) and many species await specific germination cues associated with disturbance before mass germination ( Menzel and Wilson 1969; Kak et al. 2015: R. L. Barrett and M. D. Barrett, pers. obs.), whereas some species, including S. gossypiifolia , appear to have no dormancy ( Siepe et al. 1997; Anjah et al. 2012). Thus revisiting known populations in which all genetic diversity at the site has been reduced to the soil seedbank is not uncommon. This can make population level studies challenging as specimens are only available under particular conditions, such as specific fire history at a localised scale. Many species therefore remain poorly known in many parts of the world. An advantage however, is that seeds from herbarium specimens can commonly be germinated ( Craven et al. 2003, 2016; Krapovickas and Fryxell 2004).
Animal associations with these plants are similarly poorly known. However, at least two hibiscus-flower flies are known to be associated with species of Sabdariffa ( Barker 2005) and many more such specific associations are likely to exist. Flower beetles are also commonly observed on species of this genus, the beetles commonly consuming the soft flower parts after these have shrivelled, with beetles often becoming trapped inside ( Kirejtshuk and Lawrence 1999; Simon et al. 2021). Whether or not this commonly observed process has an influence on pollination remains largely unknown. However, this would be consistent with other beetle pollination mechanisms in groups including arum lilies, in which beetles may be trapped inside flowers for extended periods and achieve pollination ( García-Robledo et al. 2004; Sayers et al. 2021). The closing of the flowers in many African, Asian and Australian Sabdariffa species appears to be primarily associated with self-fertilisation and is described in detail for S. cannabina and S. gossypiifolia by Howard and Howard (1911). Menzel et al. (1983 a) concludes that most of the American species are most likely to be bee pollinated, lacking the red basal petal spot found in many other species and lacking the selfing mechanism described above. Menzel et al. (1983 a) also notes that S. uncinella (Moç. & Sessé ex DC.) M.M.Hanes & R.L.Barrett appears to be adapted for hummingbird pollination, as the red flowers form a narrow tube and the anthers are clustered towards the style apex. Ruan (2010) and Ruan et al. (2010) provide reviews of the role of style curvature in guiding pollinators to specialised Hibisceae , including S. uncinella .
Species-level taxonomy
Species-level taxonomy of Hibiscus Section Furcaria has been further challenged by difficulties associated with the collection of high quality specimens. Once collected as herbarium specimens, Malvaceae are highly susceptible to mould and insect attacks in tropical environments and therefore the collection of high quality material is often difficult to achieve ( Knight et al. 2024). Species in this group are also often very spiny and thus not attractive to collectors. The ephemeral nature of these species in the landscape also means that repeat visits to sites may be required to collect complete specimens and therefore representation in herbaria can remain poor or patchy.
Morphologically there is a great deal of similarity among most of the species in Sabdariffa , with a few morphologically anomalous species that are nevertheless confidently included. These include the enigmatic S. kirstyae (Craven) McLay & R.L.Barrett , known from two very narrow locations in northwestern Australia, growing in shallow soils over sandstone ‘pavements’ ( Craven et al. 2016). This species differs from all other Australian species in being glaucous and otherwise completely glabrous, and in having yellow flowers, whereas almost all other species in this region have pink flowers. Therefore the superficial differences are very striking. However, the characters of the calyx, aculei, leaves and flowers are all consistent with placement in section Furcaria , where this species was originally named in 2016 ( Craven et al. 2016).
This paper mostly accepts the recently published revision papers as authorities for species concepts, with only minimal modifications and addition of recently described species ( Wilson 2006; Krapovickas 2006, 2013; Mwachala 2009; van der Burg 2013; Craven et al. 2016; Wannan 2022, 2024). We have attempted to update type citations to link to digitised type specimens where available and add barcodes to specimen citations, to make the location of these materials easier for future workers. Many lectotypes are designated to fix the applications of names. Previously published keys to species in regional areas are updated to include current names in Sabdariffa and additional species not included in the original versions.
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