Pollen of Hawaiian Cyrtandra (Gesneriaceae) including notes on Southeast Asian taxa

Pollen of 30 species and 12 hybrids (88 samples in total) of Hawaiian Cyrtandra, covering all 6 sections recognized on the Hawaiian archipelago, was examined using light, scanning and transmission electron microscopy. Hawaiian Cyrtandra is stenopalynous. The pollen grains are binucleate, isopolar, small-sized and 3-colporoidate (very rarely 4-colporoidate). In equatorial view they are spheroidal, in polar view circular or semiangular. The tectum is mostly microreticulate with brochi of different sizes (heterobrochate), very rarely reticulate or perforate. Supratectal elements are lacking. Some variation can be observed in number and diameter of the lumina. Palynological features of most of the investigated taxa tend to overlap and thus are not very helpful in supporting the infrageneric division of Cyrtandra on Hawaii. Pollen viability of hybrids, which is said to be reduced occasionally, was examined and found to be high with rates of 70 to 99%. Therefore, reduced pollen viability is not a reliable character for designating hybrid status. Asian Cyrtandra is eurypalynous. For this study, 19 species, originating from the Malay Peninsula and Borneo, have been investigated. Two exine types, differing in sculpture and structure, can be distinguished: 1) tectum microreticulate-reticulate, supratectal elements lacking, and 2) tectum microreticulate-perforate with numerous conical supratectal elements. The number, diameter and shape of lumina provide further important diagnostic features.