Description of five new species of the Madagascan flagship plant genus Ravenala (Strelitziaceae)

Madagascar’s emblematic traveller’s tree is a monospecific genus within Strelitziaceae, the family of the South African bird of paradise. Until now, this endemic genus consisted of a single species: Ravenala madagascariensis Sonn., which is grown everywhere in the tropics as an ornamental plant. The plant is immediately recognizable for its huge fan-forming banana-like leaves and is locally referred to in Magagascar by several vernacular names. “Variants” have been mentioned in the literature, but without any attempt to recognize formal taxa based on diagnostic features. In this paper, we formally describe five new species and fix the application of the name R. madagascariensis to the populations growing on the eastern coast of Madagascar, with the epitype growing in the marshy Fort-Dauphin area in the south. This paper has numerous implications for conservation biology and other domains of life sciences, due to the importance of this genus for the conservation of Madagascan ecosystems, the ornamental plant trade, as well as for its invasive status in several tropical areas.

Ravenala Adans. 1 , the traveller's palm or traveller's tree (l'Arbre du Voyageur in French, ravinala in Malagasy), is a member of the Strelitziaceae, a family within Zingiberales order whose evolutionary history is still not completely understood 2 . Strelitzia Banks 3 , the most species-rich genus in the family, has received considerably more attention than the other two monotypic genera Phenakospermum Endl. 4 and Ravenala. Synflorescences of Ravenala are distichous and monopodial, and possess a stiff basal bract enclosing 5-20 successive bracts, each one encasing a contracted monochasium (a cincinnus); the synflorescence is itself sometimes complemented by a basal leaf-like bract. Each element of the cincinnii comprises a petal-like bracteole encasing a single flower along with the remaining of the cincinnus, each flower being perfectly hermaphroditic and not varying with their position on the inflorescence. The flower structure of Ravenala has been interpreted variously in the literature, Perrier 5 describing it as similar to a Musa L. flower with five true segments. However, the perianth is more aptly described as consisting of three petaloid sepals and three petals 6 (two fused sheathing the immature stamens which mechanically need to be freed to liberate the anthers, and one free petal, whose morphological characteristics are of taxonomic importance for distinguishing the various species). The flowers contain six free stamens and a style that is roughly as long as the perianth. The fruit is a dehiscent dry woody trilocular capsule, the shape of the outer parts being of taxonomic significance. Ravenala seeds are attached to a fatty aril which has a distinctive bright ultramarine blue color (varying from deep ultramarine blue to sky blue depending on the maturity), which contrasts with the orange aril found in the other genera of Strelitziaceae (the South American endemic Phenakospermum and the South African Strelitzia). The adaptive significance of this difference may be linked to the dispersers of the seeds, the bright orange aril being documented as an adaptation to bird dispersal, while the blue color can be an adaptation to mammal dispersal. Studies have mentioned that some lemurs see only blue and green [7][8][9] , or have linked the bright blue aril of Ravenala to the fact that perception of this color has been maintained by evolution in some Madagascan nocturnal lemurs such as aye-ayes 10 . However, Kress 11 has also described Ravenala seed dispersal by birds. The morphological and ecological heterogeneity of wild Ravenala has been mentioned in several studies [12][13][14][15] , which were the first to consider scientifically these morphological variations. One of the differences highlighted is the seemingly variable suckering ability of Ravenala. This genus is usually represented as a tall suckering plant with leaves forming a perfect fan, and this can easily be appreciated from the many cultivated specimens throughout the world. However, some native Malagasy variants of the genus appear consistently devoid of suckers 13 , even when cultivated ex situ, while others consistently form suckers. Producing basal suckers is regarded by Tomlinson 16 as a feature of the order Zingiberales, with the genus Ensete Bruce ex Horan. 17 being the sole exception (bud neoformation can be artificially triggered in Ensete 18 after removal of the main bud, but this is not true "suckering" from existing dormant buds). Solitary (non-suckering) Ravenala taxa are thus another exception in presenting a monocaulous monopodial architecture (Corner model 19 ) within a suckering order (Tomlinson model 19 ).

Results
Several morphotypes within Ravenala have been observed throughout Madagascar [12][13][14][15] , but the taxonomic study of this genus had always been impaired by the extreme difficulty of collecting these enormous plants plus the added difficulty accessing most areas in Madagascar, leading to a paucity of adequate specimens in natural history collections. Our own field and herbarium specimen observations of the various morphotypes led us to recognize and distinguish six stable units defined by observable characteristics (i.e. species), consisting of five new species in addition to Ravenala madagascariensis. Thus, the total number of species recognized in Ravenala is now similar to the number of species in its sister genus Strelitzia 2 from southern Africa. Although the large Strelitzia species are difficult to distinguish when not in flower, Ravenala species can be identified when not flowering as the characters we used to define our species are observable at different developmental stages (young plants, nonfertile adults, flowering and fruiting plants, distinct flowering periods). While the distribution of the genus in Madagascar and the exact location of our type specimens can be mapped (Fig. 1), the exact extent of occurrence of each species is difficult to assess due to the aforementioned lack of available specimens. For example, in the Manombo area (eastern Madagascar), two variants are listed (the single-trunked tokam-pototra and the suckering maroanaka) 20 , but no specimens are available for scientific scrutiny to allow us to assign them to one of the taxa described here. One of the solitary morphotypes called malama from the Andasibe area (our R. blancii), may correspond to the variant called locally fontsy ala discovered 21 in the Forest Reserve of Ranomafana (200 km to the south of Andasibe, at the same elevation range), but again we lack specimens to attest the presence of this taxon. This suggests that this peculiar malama variant could be present across a large part of the eastern coast of Madagascar, at elevations ranging from 600 m to 1,100 m 12,20 . All species except Ravenala agatheae  www.nature.com/scientificreports/ are distributed along the eastern coast of Madagascar (Fig. 1), and their distribution range seems to follow an elevation gradient 20 , with R. blancii and R. hladikorum being found at the highest elevations, R. grandis at midelevation, and R. madagascariensis and R. menahirana being found at sea level (of these, only R. madagascariensis appears to be distributed all along the coast). By contrast, Ravenala agatheae from the north-western part of Madagascar is not found elsewhere on the island (Fig. 1). The major traits used to distinguish these species, as detailed in the identification key and the taxonomic treatment, are: plants suckering or strictly solitary; the flowering period; traits pertaining to the petiole such as the presence of various papery appendages or color patterns; the inflorescences; the flower structure (especially the length of the free petal vs. the lentgh of the two fused petals); and shape and structure of the fruit apices (Fig. 2).    Identity of Ravenala madagascariensis Sonn. -Figs. 2d, 3d, 4d, 5d-In the absence of a specimen undoubtedly collected or seen by Sonnerat (Commerson's specimens, collected in Mauritius and preserved in both Jussieu's and Lamarck's herbaria at the Paris herbarium (P-JU and P-LAM), might actually be part of original material), we decided to lectotypify from plates 124, 125 and 126 of the protologue in Sonnerat's valid publication 24 of the species. On page 225, Sonnerat 24 mentions that the plant originated from Madagascar but was transported and established in Mauritius (known at the time as Isle de France) at the "Jardin des Pamplemousses". We observed plants growing in this garden as well as naturalized plants occurring in the wild in Mauritius; all the plants we saw suckered and possessed the characteristic pointed conical fruits also observed in the Fort-Dauphin population. Sonnerat also specified that the original plant grew in marshy areas, which corresponds exactly to the coastal populations that can be found on the eastern coast of Madagascar (i.e. the "Horonorona" variant of Blanc et al. 13 ). Plate 126 shows the typical mature infructescence of the species, with the space between bracts increasing before releasing the seeds (unlike other species of Ravenala). However, the "tree" pictured on plate 124 is a non-suckering plant, which in our opinion can be explained as artistic license on the part of the illustrator, as all the plants observed in Mauritius consistently sucker, like the plants growing in the south-eastern marshy areas. We also decided to designate an epitype with a documented locality in Madagascar (the material in P-JU and P-LAM does not bear a precise indication of locality) to fix the application of the name R. madagascariensis to the populations occurring in the marshy areas surrounding Fort-Dauphin, where only one morphotype is known.
Ecology Ravenala madagascariensis is a low-altitude species restricted to swampy areas of the eastern coast of Madagascar. Populations outside of Madagascar on nearby islands are reputedly non-indigenous 24 .
Note This emended description for R. madagascariensis was drawn up from our own observations and collections, and was made comparable point by point to the descriptions of the five new species presented below, along with a dichotomous identification key to all six species. Diagnosis Similar to Ravenala madagascariensis but differs in its dark green narrower laminae, tricolor petioles with very developed dryish petiole sheath margins, very waxy petioles, the persistence of older infructescences for several years, a purple stripe on the bract margin, longer bracts, a whitish perianth, brown blotches on its mature fused petals, the bracteole apex tinged with pink, an ovoid pointed stigma, dense infructescences, smaller inflorescences, the free petal much shorter than the fused petals, and an end of year flowering period.
Distribution Plants restricted to Madagascar, growing in the north-western part of the island. We observed it growing from the southern part of the Diego Suarez area (on the hills along the road leading to Tsingy Rouge   33 . Ecology This species is adapted to seasonally dry and warm coastal habitats, growing on slopes at low elevations in north-western coastal areas of Madagascar, from Antsiranana (Diego-Suarez) down to the Melaky region in the Mahajanga province.
Etymology This species is named after to the first author's wife, Agathe Haevermans, a botanical illustrator at the Muséum National d'Histoire Naturelle, who helped discover this species in the field with the collecting team and who contributes greatly to botany by producing illustrations of new taxa from biodiversity hotspots such as Madagascar.

Preliminary IUCN assessments
We propose a Data Deficient status for R. blancii; further fieldwork is required to understand its precise distribution and the status of its populations 33 .
Ecology High-elevation species found in eastern rainforests at elevations between 600 and 1,100 m. The species seems to favor cool tropical humid and shady conditions. Etymology This species is named after Dr. Patrick Blanc, world renowned botanist, plant ecologist and street artist, inventor of the planted vertical walls known as "Mur Végétal" and who first recognized the sheer originality of the juvenile phases of this peculiar taxon.
Note The strong leaf dimorphism between juvenile and adult forms is characteristic of this species 13 , a phenomenon which is not present in the other taxa. The base of the juvenile plant usually grows buried in the leaf litter due to the action of traction roots 13 , its decurrent leaves (Fig. 7) giving it the aspect of a bird's nest fern. Diagnosis Similar to Ravenala madagascariensis but differs in its non-suckering habit, much larger dimensions, very thick leathery laminae, very waxy dark green-yellowish petioles, much larger bracts and overall dimensions, whitish/pure white perianth, strong reddish-pink stripes on its bracteoles, cylindrical stigma without basal constriction, stamens much shorter than perianth, and fruit with a truncated apex.

Preliminary IUCN assessments
We propose a Data Deficient status for R. grandis; further fieldwork is required to understand its precise distribution and the status of its populations 33 .
Ecology This species seems to favor growing in low discontinuous forests on inselbergs 12 and thrives in secondary degraded vegetation on the slopes of eastern rain forests.
Etymology The name of this species is in reference to its stature and habit, the most robust species of Ravenala known.
Ravenala hladikorum Haev., Razanats., V. Jeannoda & P. Blanc sp. nov. -Figs. 2f, 3f, 4f, 5f Diagnosis Similar to Ravenala madagascariensis but differs in its non-suckering habit, the alternate positioning of its adult laminae, its dark green leaves, non-waxy petioles with their very papyraceous petiole sheath margins, more than 1 cm long, smaller lamina dimensions, smaller number of simultaneously live inflorescences, purple stripe on bracts and on bracteoles, non-waxy inflorescences, smaller inflorescences, dense infructescences, truncated fruit apices, and short flowering period from November to December.

Preliminary IUCN assessments
We propose a Data Deficient status for R. hladikorum; further fieldwork is required to understand its precise distribution and the status of its populations 33 .
Ecology High-elevation species found in eastern rainforests at elevations between 600 and 1100 m. The species seems to favor cool tropical humid and shady conditions. Etymology This species is named in honor of Annette and Claude-Marcel Hladik from the Muséum National d'Histoire Naturelle in Paris, who dedicated their lives to the study of Madagascan biodiversity and contributed greatly to the discovery of this species.
Distribution Appears to be restricted to the east coast in the area around Analalava-Foulpointe up to the Mananara-Avaratra area. Two human observations from Marojejy (North-East) and Tampolo (Masoala) seem also to be this species. Restricted to Madagascar.
Preliminary IUCN assessments We propose a Data Deficient status for R. menahirana; further fieldwork is required to understand its precise distribution and the status of its populations 33 .
Ecology This coastal forest-dwelling species favors low-elevation tropical humid conditions in the Analalava-Foulpointe area, extending north to Mananara-Avaratra area, and maybe up to Marojejy.
Etymology The name of this species is in reference to one of its local names "menahirana", given to the species in the Analalava-Foulpointe area and meaning "red ravenala".
Identification key to the species of genus Ravenala.

Discussion
The five new species described in this paper can be easily identified at both young and adult stages from distinctive morphological characters defined from petiole sheath margins, petiole coloring and morphology, suckering or solitary habits and flower and fruit traits. The main stable character distinguishing these species 13 is the ability to produce suckers (R. agatheae, R. madagascariensis) like other members of Zingiberales, or its absence (i.e. strictly monopodial) (R. blancii, R. grandis, R. hladikorum, R. menahirana) ( Table 1). The laminae arrangement in space is also of taxonomic significance, especially for the juvenile R. blancii, whose leaves, although distichally inserted, have laminae distributed in such a way as to form a torus (Fig. 7b), which is likely to be an adaptation to the low light intensity of the forest floor where it germinates 12 . At early stages, this species, with its decurrent laminae arranged in a torus, bears a striking resemblance to the bird's nest fern (Asplenium nidus Linnaeus 36 ). The genus occurs across a variety of bioclimates and habitats, with each species seemingly favoring a specific niche. Both suckering species occur at sea level and on low-elevation coastal hills, with the well-known R. madagascariensis being documented in the coastal marshes of the east coast of the island, whereas R. agatheae is documented in the north-western part of the island (Fig. 1). The comparatively drier climates in which the latter occurs may favor the persistence on the "trunk" of a blanket of dry petioles and infructescences which may be involved in some form of fire resistance. By contrast, the solitary species are all distributed on the eastern part of Madagascar from sea level to around 1000 m elevation, on slopes originally covered by forests. Their distribution likely follows an elevation gradient, with R. menahirana found in now rare sea level coastal forests, R. grandis in mid-elevation (300-500 m) forests on steep inselbergs slopes (see Figs. 2, 3, and 4 in Blanc et al. 12 ), while R. blancii and R. hladikorum are found in sympatry in the shade in high elevation (1000 m) rain forests 12 . Further research on the population genetics, pollination and seed dispersal of the formerly monotypic Ravenala would be essential within this new six-species framework. This genus may also prove to be a good model for studying sympatric speciation and provide a better understanding of the interactions of the endemic fauna of Madagascar with this flagship taxon.

Methods
Taxonomic treatment follows the International Code of Nomenclature (ICN) for algae, fungi and plants 37 (Shenzhen Code). Specimen citations follow the CETAF (Consortium of European Taxonomic Facilities) guidelines 38 . Specimens were deposited in natural history collections as indicated by their international acronym 39 . Descriptive terms follow standard botanical terminology 40 . Macromorphological characters (see a summary in Table 1 www.nature.com/scientificreports/ were studied in the field and in the laboratory from specimens the authors collected, according to national and international standards and regulation, and from specimens held in several herbaria where Ravenala specimens are deposited (G, K, MO, P, TAN, US) 39 . The distribution maps (Fig. 1) were prepared with the software R, using coordinates from our own collections and observation data, from other available specimens (n = 19 gatherings, represented as n = 40 sheets), as well as from the www.inaturalist.org website observations we managed to identify (n = 83). We used the triple equality sign ( ≡ ) to indicate homotypic synonyms, the equal sign (=) to indicate heterotypic synonyms and the 'en-dash' (-) to indicate invalid names. All protologues of relevant names were consulted to establish the nomenclatural synopsis.  www.nature.com/scientificreports/ Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.