Pollen morphology of species in Gesnerioideae (Gesneriaceae) and related species: morphological variations and taxonomic importance

Gesneriaceae is subdivided into three subfamilies: Sanangoideae, Gesnerioideae and Didymocarpoideae. This classification has been investigated and the monophyly of subfamilies and their respective tribes and subtribes has been supported by recent phylogenetic studies. Gesnerioideae contains 77 genera and more than 1200 species, distributed exclusively in the Neotropics, with the exception of Titanotrichum Soler. and some Coronanthereae taxa. Its species present flowers with a very variable set of colors and shapes and a diversity of pollination syndromes. The objective of this study was to characterize and describe the pollen morphology, providing detailed pollen structure and ultrastructure data for the species of this subfamily and closely related species in order to expand knowledge and provide subsidies for the taxonomic delimitation of the groups. The pollen grains of 99 species of Gesneriaceae belonging to 43 genera were analyzed, 84 of which are from Gesnerioideae, whose representative tribes are: Titanotricheae (Titanotrichum Soler.), Beslerieae (Besleria L. e Gasteranthus Benth.), Coronanthereae (Asteranthera Hansl., Coronanthera Vieill. ex C.B.Clarke, Mitraria J.F.Gmel., Rhabdothamnus A.Cunn. e Sarmienta Ruiz & Pav.) and Gesnerieae (Achimenes Pers., Codonanthe (Mart.) Hanst., Codonanthopsis Mansf., Columnea L., Corytoplectus Oerst., Diastema Benth., Drymonia Mart., Episcia Mart., Eucodonia Hanst., Gesneria L., Glossoloma Hanst., Gloxinella (H.E.Moore) Roalson & Boggan, Gloxiniopsis Roalson & Boggan, Kohleria Regel, Monopyle Moritz ex Benth. & Hook.f., Moussonia Regel, Nautilocalyx Linden ex Hanst., Nematanthus Schrad., Neomortonia Wiehler, Paliavana Vell. ex Vand., Pearcea Regel, Phinaea Benth., Rhytidophyllum Mart., Seemannia Regel, Sinningia Nees, Sphaerorrhiza Roalson & Boggan and Vanhouttea Lem.). In addition to these, 15 species of Trichosporeae were analyzed: Aeschynanthus Jack, Boea Comm. ex Lam., Cyrtandra J.R.Forst. & G.Forst., Deinostigma W.T.Wang & Z.Y.Li, Didymocarpus Wall., Primulina Hance, Ramonda Caruel and Streptocarpus Lindl., and as an outgroup to Gesneriaceae, Peltanthera floribunda Benth., a species closely related to the family. The pollen material was obtained from specimens deposited in herbaria ESA, G, HUFABC, INPA, P, SP and Z and from species cultivated at Sítio Primavera in Mogi das Cruzes, SP. Pollen grains were acetolyzed, measured and photographed under light microscopy. The sexine sculpture and exine structure were electrographed and analyzed by scanning and transmission electron microscopy, respectively. Quantitative data were analyzed using descriptive and multivariate statistics. Structural and ultrastructural qualitative data of pollen grains were described. The pollen grains of the analyzed species are monads and isopolar, they vary in terms of size, amb, shape, type and number of apertures (3-colpate, 3-colporate, 4-colporate), and exine ornamentation (tectate perforate, microverrucate, nanoverrucate-nanoechinate, scabrate-perforate; semitectate, foveolate, microreticulate, microreticulate-rugulate, microreticulate-verrucate, microreticulatescabrate, microreticulate-nanoechinate, reticulate, reticulate-nanoechinate, bireticulate, homo ou heterobrochate). In addition to the qualitative morphological differences observed, the quantitative data of pollen grains indicate that size is an important pollen character for the distinction of groups and may be related to the length and width of the colpi in certain species. Therefore, this study confirms Gesnerioideae as eurypalynous and indicates out pollen characters that help in the delimitation of groups at tribal, subtribal, generic and even specific levels, constituting useful tools for taxonomic studies of this subfamily and related species. (AU)