Morphological and anatomical analyses of rheophytic Rhododendron ripense Makino (Ericaceae)

Abstract

The comparative morphology and anatomy of the leaves of the rheophytic Rhododendron ripense and the closely related inland species Rhododendron macrosepalum were examined. The leaf of R. ripense is thinner than that of R. macrosepalum, with leaf length to width ratios (leaf index) of 2.92 and 1.91, respectively. Moreover, the leaf of R. ripense consists of fewer cells than the leaf of R. macrosepalum, suggesting stenophyllization of R. ripense caused by the decreased number of cells. In addition, leaf thickness and the number of stomata per leaf of R. ripense were significantly greater than those of R. macrosepalum, but the density of the short glandular pilose hairs on the leaf of R. ripense was lower. The observed morphological differences between the two species may be explained by certain aspects of the riparian environment, such as high irradiation and frequent flooding after heavy rainfall, to which R. ripense is exposed.

Morphological and Anatomical Variations in Rheophytic Ecotype of Violet, Viola mandshurica var. <i>ikedaeana</i> (Violaceae)

“…Previous studies of F. japonicum var. luchuense and R. ripense showed that individuals growing on riverbanks had larger leaf thicknesses than did those of inland plants [9,14,23]. Taken together, these findings indicate that increased leaf thickness is a general tendency among rheophytes-V. mandshurica var.…”

“…ikedaeana, suggesting that the same stenophyllization process operates independently among rheophytic taxa. Previous anatomical studies have shown a decreased number of cells in all angiosperm rheophytes [9][10][11][12][13][14]23], indicating that this is a common mechanism contributing to stenophyllization. Based on angiosperm phylogeny [15][16][17][18], variation of cell size in the rheophytic Ad.…”

“…This anatomical mechanism of stenophyllization is similar to that previously reported for R. ripense [13], R. indicum (L.) Sweet f. okutami T. Yamaz. [14], and F. japonicum var. luchuense [9,23].…”

“…Meanwhile, the rheophytic types of Rhododendron indicum (L.) Sweet f. otakumi T. Yamaz. and R. ripense Makino (Ericaceae) were found to evolve through a decrease in the number of leaf cells [13,14]. All of these anatomical studies were conducted on plants in the asterid group, according to angiosperm phylogeny [15][16][17][18].…”

Phylogeographic analysis suggests two origins for the riparian azalea Rhododendron indicum (L.) Sweet

“…Plant populations growing along rivers are subject to disturbance due to flooding after heavy rains, and this can have a significant effect on plant survival. The narrow and thick leaves of riparian plants, referred to as rheophytes, growing along rivers are considered to be a consequence of adaptation enabling them to tolerate spates of water (van Steenis 1981(van Steenis , 1987Tsukaya 2002;Mitsui et al 2011;Ueda et al 2012). The plants grow at or above water level, and experience stress due to water flow when it rains heavily and the water level rises.…”