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 Pančić & Petrović, and R. serbica Pančić (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.

Comparative Pollen Morphological Analysis and Its Systematic Implications on Three European Oak (Quercus L., Fagaceae) Species and Their Spontaneous Hybrids

“…Other researchers proved that hybrids can have pollen size similar or smaller than their parents [53, 55, 57, 60, 62, 66, 84, 85]. Last but not the least, there are also cases where some hybrids are characterised by pollen grains larger than parental species, while others—smaller [59, 61, 64]. …”

Resurrection plants of the genus Ramonda: prospective survival strategies – unlock further capacity of adaptation, or embark on the path of evolution?

“…Within this area, on two localities in South East Serbia (Jelašnica and Sićevo gorges), they form sympatric populations within which they hybridize (Stevanović et al, 1986, 1987; Siljak-Yakovlev et al, 2008a; Lazarević et al, 2013). …”

“…Thus, the existence of hybrid individuals between R. nathaliae and R. serbica suggest that completely effective barriers for their intercrossing are still not in place (Lazarević et al, 2013) and reveals complex processes of hybridization, introgression, and genome duplications (Siljak-Yakovlev et al, 2008b). …”

“…Both Ramonda species have disjunct zones to the north-east (the Central Balkans) of their respective ranges that belong to the Black Sea river system. Within this area, on two localities in South East Serbia (Jelašnica and Sićevo gorges), they form sympatric populations within which they hybridize ( Stevanović et al, 1986 , 1987 ; Siljak-Yakovlev et al, 2008a ; Lazarević et al, 2013 ).…”

Pollen Morphology of Herbaceous Peonies with Different Ploidy Levels

“…LEVEL. Several studies have determined that the size of pollen grains is an effective parameter for the analysis of ploidy level (Lazarevic et al, 2013;Marinho et al, 2014). Consequently, pollen size and shape may serve as a reference index in the identification of ploidy levels, as has been shown by Liu et al (2003), Yan et al (2005) and Wang et al (2015) in watermelon [Citrullus lanatus (Thunb.)…”