Abstract
Background Stelis (Orchidaceae) encompasses approximately 1100 species of epiphytic orchids distributed throughout the Neotropics, with the highest diversity in Andean South America. Sixty-two species were recorded previously in Mexico.MethodsWe formally describe here Stelis zootrophionoides as a new species from Chiapas, Mexico. To determine its systematic position, we conducted a morphological comparison with other members of Pleurothallidinae and a phylogenetic analysis of nucleotide sequences from the plastid matK/trnK and trnL/trnF regions, as well as the nuclear ribosomal ITS region for 52 species of Pleurothallidinae. Sequences of 49 species were downloaded from GenBank and those of three species, including the new taxon, were newly generated for this work. The new species is described and illustrated; notes on its ecological preferences and a comparison with closely related species are presented.ConclusionsThe new species, known only from one location and apparently restricted to the cloud forest in the central highlands of Chiapas, Mexico, is considered a rare species. This small epiphyte is unique among the Mexican species of Stelis by the combination of dark purple flowers with the distal third of the dorsal sepal adhered to the apices of the lateral sepals, which are partially united into a bifid synsepal, leaving two lateral window-like openings, and sagittate labellum. Stelis jalapensis, known from southern Mexico and Guatemala, also has the apices of the sepals adhered to each other, but it is distinguished by its larger flowers with lanceolate, acute dorsal sepal, completely fused lateral sepals (i.e. the synsepal is not bifid), and oblong-elliptic labellum. The phylogenetic analysis shows that S. zootrophionoides is closely related to other Mexican Stelis and corroborates previous suggestions that fused sepal apices have arisen independently in different lineages of Pleurothallidinae.
Highlights
Stelis Sw. (Orchidadeae) is the most species-rich genus in subtribe Pleurothallidinae [1,2]
During a field trip in the central highlands of Chiapas, we collected specimens of a small plant belonging to subtribe Pleurothallidinae in which the distal part of the dorsal sepal was adhered to the apices of the lateral sepals, but otherwise was separated from them to form two lateral window-like openings
Flowers 4– 8.1 mm long, resupinate, slightly pendent, the apex of the dorsal sepal adhered to the apex of the synsepal, forming two lateral, window-like openings; floral segments and column creamy yellow or greenish yellow, densely blotched with dark purple, anther white
Summary
Stelis Sw. (Orchidadeae) is the most species-rich genus in subtribe Pleurothallidinae [1,2]. (Orchidadeae) is the most species-rich genus in subtribe Pleurothallidinae [1,2]. Lithophytic, or rarely terrestrial orchids restricted to the American tropics, distributed from southwest Florida and northwestern Mexico through the Antilles to Bolivia and Brazil, with the highest diversity concentrated in Andean South America [1,2]. Sixty-two species of Stelis were recorded previously from Mexico [4,5,6]. During a field trip in the central highlands of Chiapas, we collected specimens of a small plant belonging to subtribe Pleurothallidinae in which the distal part of the dorsal sepal was adhered to the apices of the lateral sepals, but otherwise was separated from them to form two lateral window-like openings. Stelis (Orchidaceae) encompasses approximately 1100 species of epiphytic orchids distributed throughout the Neotropics, with the highest diversity in Andean South America. Sixty-two species were recorded previously in Mexico
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