Pollen and seed morphology of resurrection plants from the genus Ramonda (Gesneriaceae): relationship with ploidy level and relevance to their ecology and identification

Abstract

The pollen and seeds of 3 paleoendemic resurrection species, Ramonda myconi (L.) Rchb. (Iberian Peninsula), R. nathaliae Pancic & Petrovic, and R. serbica Pancic (Balkan Peninsula), as well as of natural hybrids between the 2 last species, have been analyzed using light and scanning electron microscopy. Their general structural differences, taxonomic and phylogenetic significance, pollen viability, and seed germination capacity, as well as the correlation of pollen and seed characteristics and plant ploidy levels, have been studied. The pollen grains are small (R. myconi , R. nathaliae) to medium (R. serbica) in size, ranging from 10 to 28 µm, and 3-colporate, isopolar monads with microreticulate-perforate exine. Seeds are small, 309 to 1000 µm long and 80 to 425 µm wide, elongated, with a reticulate surface and auriculate ornamentation. Micromorphologies of the pollen exine ornamentation and seed surface revealed significant differences among the 3 species. Pollen from hybrid individuals was heterogeneous in size and morphology, and the germination of their tiny seeds was very low. A strong correlation was found between pollen size, DNA content, and chromosome number. The environmental influence on pollen and seeds of 3 species and especially of the R. nathaliae population growing on serpentine is also discussed.