The Leafless Vanilla Species-Complex from the South-West Indian Ocean Region: A Taxonomic Puzzle and a Model for Orchid Evolution and Conservation Research

Abstract

The pantropical genus Vanilla is a member of the Orchidaceae family, one of the largest and most diverse families of angiosperms in the world. It originated in America and differentiated in America, Africa, and Asia. About 132 species of Vanilla have now been accepted since the discovery of the genus. Within the Vanilla genus, leaflessness has appeared at least three independent times, in Africa, Asia, and America as an adaptation to drought conditions. The South-West Indian Ocean (SWIO) region, a biodiversity hotspot for orchids, is home to seven leafless species. Chloroplast markers failed to differentiate species within this recent SWIO clade. Morphological traits used for description are very similar between species and do not provide reliable identification. Moreover, some of the species have overlapping flowering periods and geographic distribution in Madagascar, increasing the probability of finding some sympatric species and, therefore, hybrids. Leafless Vanilla species from the SWIO islands are thus an excellent model for understanding the evolution of orchids. For their conservation, and to confirm the identity of these leafless species, an integrated approach with classical taxonomy using a large number of samples, intense fieldwork on biology and ecology, and molecular studies using variable markers is necessary.

Drivers of population divergence and species differentiation in a recent group of indigenous orchids (Vanilla spp.) in Madagascar

“…Our results showing the existence of possible hybrids between some sympatric species in the west of Madagascar reinforces this hypothesis, as also demonstrated for two sympatric leafless Vanilla species in Puerto Rico ( V. barbellata and V. claviculata ) (Nielsen, 2000) for which the occurrence of hybrids suggested the same pollinator. In the genus Vanilla , in America, the known pollinators of wild species of the V. planifolia and V. pompona groups are similar, and they are all orchid‐bee species from the genera Eugloss a and Eulaema (Andriamihaja et al., 2020).…”

“…Eight populations assumed to represent all clusters from genetic structuring analysis were targeted during their flowering season based on bibliographical information (Andriamihaja et al., 2020): MSL and MND (October), BFD and MDF (November), and AJA, ATD, MLT, and AND (December) (Table ). One herbarium specimen of each genetic group was deposited at the herbarium of the Botanical and Zoological Park of Tsimbazaza (N°51/20/MESupRES/SG/DGRS/PBZT/Flore).…”

“…The Vanilla Plumier ex Miller (34.6 Ma, Bouetard et al, 2010) belongs to the Orchidaceae, one of the most diverse family of angiosperms (Bouetard et al, 2010;Gigant et al, 2011). It comprises about 132 species (Andriamihaja et al, 2020) distributed throughout tropical forests between the 27th north and south parallels, but are absent in Australia (Gigant et al, 2011;Portères, 1954). With nine wild Vanilla species described, the Southwest Indian Ocean (SWIO) region ranks fourth among the richest regions and first in terms of leafless species, most being located in Madagascar (Gigant et al, 2011;Portères, 1954).…”

“…Within the SWIO region, seven leafless species can be found, ensuing from the adaptation of an African leafy ancestor to xeric conditions (Bouetard et al., 2010). As they are part of a recent monophyletic group (4.4 Ma) (Bouetard et al., 2010), these species retain numerous similarities in their morphology (Allorge‐Boiteau, 2013; Andriamihaja et al., 2020; Cribb & Hermans, 2009; Portères, 1954; Soto‐Arenas & Cribb, 2010), making their identification difficult. Chloroplast DNA phylogenetic analyses also failed to distinguish the various species from this group (Bouetard et al., 2010).…”

Vanilla beyond Vanilla planifolia and Vanilla × tahitensis: Taxonomy and Historical Notes, Reproductive Biology, and Metabolites

“…Mill (1754) (Orchidaceae) consists of 140 species, most of which are scientifically and commercially unexplored [ 1 , 2 ]. This genus, represented by perennial vines, is characterized by a thick and fleshy stem, a monopodial growth habit ( Figure 1 ), aerial hairless roots growing at each node, and underground hairy roots, absence of pseudobulbs, alternate leaves, axillary inflorescence, flowers with lips partially adnate to the column, versatile anther that is generally saddle-shaped, and fruits with encrusted seeds [ 3 , 4 ]. Certain species of this genus are commercially designated as natural vanilla, a spice made from the fruit of orchid vines, which has a high gastronomic standard.…”