Anatomy and Morphology of Two Hawaiian Endemic Portulaca Species

The genus Portulaca is known to withstand harsh environments with its various vegetative and reproductive features. Hawaiian Portulaca species are annual or perennial herbs that rarely form shrubs. Both native and introduced Portulaca species on the Hawaiian Islands, such as P. oleracea and P. pilosa, are relatively common. However, endemic species of P. molokiniensis and P. sclerocarpa are also present although not as widespread. Among Hawaiian Portulaca species, P. molokiniensis and P. sclerocarpa have drawn attention because of their unusual vegetative and reproductive features. The relationship between these two species and other Portulaca species has been investigated in previous studies (Kim & Carr, 1990a, 1990b). P. oleracea and P. pilosa, which is widely distributed, have particularly been of focus. This is because P. oleracea has been speculated to be the parental lineage of P. molokiniensis, and P. pilosa that of P. sclerocarpa (Yun, 1989; Wagner et al., 1999). Artificial, interspecific pollinations have yielded a hybrid between the broad-leaved P. molokiniensis (2n=40) and P. oleracea (2n=54) suggesting a close affinity and polyploid nature (Kim & Carr, 1990a). Kim and Carr (1990a) have distinguished two groups of Hawaiian Portulaca species based on their chromosome ploidy level–polyploids (2n=40, 54) in broad-leaved species versus diploids (2n=18) in cylindricalleaved species. Reproductive features have been reported with variation among taxa in studies examining the reproductive biology and uniformity of Portulaca species (Kim & Carr, 1990b) as well as their cytogenetics and hybridization (Kim & Carr, 1990a). Furthermore, the Kranz anatomy, as in C-4 syndrome, has been well-demonstrated in a study investigating structural aspects of the leaves of seven Portulaca species growing in Hawaii (Kim & Fisher, 1990). In recent works, morphological and anatomical features of seeds (Kim, 2012) and pollen grains (Kim, 2013) have revealed important structural patterns among taxa. None of these studies, however, include vegetative stomata features or other features that may have been influenced by polyploidy. Thus, Anatomy and Morphology of Two Hawaiian Endemic Portulaca Species