a revision of the mexican and central american species of vanilla ...

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292 LANKESTERIANA FiGurE 1. Strict consensus from 30,090 minimal trees obtained from ITS sequences of the nuclear ribosomal DNA. LANKESTERIANA 9(3), January 2010. © Universidad de Costa Rica, 2010.
soto arEnas & drEsslEr — A revision of Central American Vanilla 293 2003), matK, and 18S topologies (Soto Arenas et al., in prep) are incongruent with the position of these two particular sequences of Vanilla and we regard them as paralogous ITS copies. Cloning in 10 PGEM a PCR product of V. cf. kaniensis Schltr. (a species from New Guinea) yield three different ITS clones which differ only in 1 and 2 DNA bases and are clustered together in the ITS phylogeny, therefore ITS is a very useful identifying tool. Other paralogous ITS sequences of Vanilla (from species of other regions) have occasionally resulted, especially when DNA has been extracted from herbarium specimens or less often from tissues dried in silica gel. No more paralogous copies of American vanillas have been detected, and both included represent the two main lineages in the genus. If they are excluded, both the defined outgroup and Vanilla become monophyletic. The paralogous sequences are largely divergent, and therefore easily identified. This is probably because the duplication event that produced them seems to have been previous to the separation of Vanilla from their related groups. The leafless group is not well-documented from Mesoamerica (see discussion in ‘Excluded taxa’); a Puerto Rican specimen of V. calyculata and another of V. barbellata were included. There are no confirmed reports of these species from Mexico or Costa Rica, respectively; in any case, it is rather surprising that leafless taxa are absent in Yucatán, very close, and with similar habitats to places in Cuba where leafless vanillas are present. The rest of the Mesoamerican vanillas belong to the group recognized by Soto (2003) as “American fragrant Vanilla spp.” Phylogeny of Vanilla is discussed in more detail in Soto (2003). What is important for identification purposes is that ITS sequences are largely species-specific, since the species form monophyletic groups with very high bootstrap support. The only exceptions are V. odorata which proved to be paraphyletic, since V. helleri and V. tahitensis are nested in it. Two samples from east of the Tehuantepec Isthmus share a different ITS sequence. Vanilla tahitensis sequences are not different from most of V. odorata, a result which is not incongruent with a the hypothesis of a recent hybrid origin of this taxon (between V. planifolia and V. odorata), as its morphology suggests. The Vanilla pompona complex has a bootstrap value of 99%. All the Mexican samples of V. pompona plus two specimens (SEL 1985-0211A and a sequence in the Gen Bank U66819) form a clade with 99% of bootstrap support. Several South American specimens of V. grandiflora form a weakly supported (63% bootstrap value) branch, and the rest of the South American specimens of V. pompona and the Costa Rican, Honduran, and Panamanian specimens of the V. pompona complex form a polytomy at the base. This structure in the V. pompona complex is congruent with the distributional disjunctions and suggests that an infraspecific classification of the species is required. In conclusion, ITS sequences are a very useful tool to separate sympatric, vegetatively indistinguishable vines like V. planifolia, V. helleri, and V. cribbiana, or to identify specimens with juvenile or etiolated vegetative characters. We suspect that one of the reasons for the lack of an important breeding effort in Vanilla has been due to the difficulties of identifying material. The origin of V. tahitensis has been much argued. These data indicate clearly that V. tahitensis is very closely related to V. odorata. Vanilla tahitensis is clearly a member of the American fragrant clade of vanilla, characterized by leafy plants and penicillate calluses, and which is absent in the Old World Tropics (as in New Guinea) where the vanillas geographically nearest to Tahiti occur), therefore the hypothesis that it was introduced recently to Tahiti is strongly supported. Since vegetatively it has much broader leaves than V. odorata, it is almost certain that it is not conspecific with this species. The flower is larger than in V. planifolia, and it is rather intermediate in all traits between V. planifolia and V. odorata. These molecular data, and other unpublished data including many more species from other areas, suggest that V. phaeantha, V. insignis, V. helleri, V. odorata, and V. tahitensis are the closest relatives of the vanilla of the commerce, V. planifolia, even much more closely related than V. pompona with which it has formed hybrids that are at present cultivated. The close relatives all have fragrant fruits and have different habitat preferences; thus they represent a pool of interesting traits with potential to be incorporated into this crop. LANKESTERIANA 9(3), January 2010. © Universidad de Costa Rica, 2010.
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