Dathe, S. & Dietrich, H.: Comparative molecular and morphological studies in selected Maxillariinae orchids. — Willdenowia 36 (Special Issue): 89–102. — ISSN 0511-9618; ©2006 BGBM Berlin-Dahlem. doi:10.3372/wi.36.36106 (available via  http://dx.doi.org/)

The phylogenetic relationships within Orchidaceae subtribe Maxillariinae s.str. were investigated by Maximum Parsimony and Bayesian analyses of nuclear ribosomal ITS1 and ITS2 DNA sequences in 27 species. While the monophyly of Maxillariinae is supported, Maxillaria in its current, narrower circumscription is clearly paraphyletic, since all presently accepted genera examined (Chrysocycnis, Cryptocentrum, Mormolyca, Trigonidium) and the former segregates Camaridium, Heterotaxis, Marsupiaria, Neourbania, Ornithidium and Pseudomaxillaria are nested within it. Camaridium, Heterotaxis and Ornithidium are, moreover, polyphyletic. The resulting molecular trees show six more or less well supported clades but are not very well resolved in their basal parts. To study character evolution, the molecular data were compared with pollinarium morphology, using scanning electron microscopy in 22 taxa, and further morphological data. The comparison indicates that most features have evolved several times independently. In growth habit a trend from caespitose to rhizomatous is found. Palynologically three morphological lines are indicated: (1) from four greater pollinia in two pairs to four smaller, equal, separate pollinia; (2) from spherical to clavate pollinia; (3) from pollinia with rugulate (sometimes gemmate, granulate, fossulate, microfoveolate) to psilate surface. A more extensive taxon sampling is needed to decide if and how Maxillaria s.l. has to be divided in smaller monophyletic genera.