||Mangroves are a group of the intertidal plants with unrelated phylogenetic affinity distributed in regions of estuaries, riverbanks or along the coastlines of tropical and subtropical areas. The four genera of tribe Rhizophoreae of Rhizophoraceae are important members of mangroves, namely Bruguiera, Ceriops, Kandelia and Rhizophora and also known as mangrove Rhizophoraceae, with a wide distribution range. Fourteen of 17 species of mangrove Rhizophoraceae distributed in the areas between the Eastern Africa to the Pacific West Coast, belong to the eastern mangrove Rhizophoraceae. |
Thirteen species of the eastern mangrove Rhizophoraceae from different populations were sampled for the studies in comparative morphology and anatomy on stipules, leaves, flowers, fruits and viviparous seedlings. In contrast, four species of three genera belong to the inland Rhizophoraceae were also sampled. Such works were emphasized on stipules and leaves.
Three kinds of sclereids were found in the stipules of Ceriops and Rhizophora, but none in Kandelia and Bruguiera. Several to hundreds colleters arranging in several series occur at the adaxial base of a stipule in Rhizophoraceae. The aggregated forms, series number, number and individual morphology of colleters are generic or specific, and could be an aid for taxonomic identification. The number and size of colleters found in the mangrove Rhizophoraceae are more and larger than those of the inland species. Additionally, the size of stipule in mangrove Rhizophoraceae is larger than those of the inland Rhizophoraceae. These characters might imply an adaptive selection of stipule and colleters in Rhizophoreae.
In this study, many of the previous discrepancies of leaf anatomical features were clarified. Meanwhile, the plasticity of leaf structure, features of sclereid ideoblasts and crystals were not previously reported. The leaves of mangrove Rhizophoraceae present thick leaves and cuticular wax, sunken and cyclocytic stomata with distinct inner and outer ridges, 2 to 8 cell-layered hypodermis, enlarged terminal tracheids, four types of sclereid ideoblasts and abundant tanniferous cells and drused crystals. All species of the mangrove Rhizophoraceae has potential to produce cork warts on both sides, but only Rhizophora has the warts mainly on abaxial side regularly. Detailed stomatal features could serve as diagnostic character in species level. On the contrary, the inland species has thin leaves with less cuticular wax, superficial anomocytic stomata, no hypodermis and enlarged terminal tracheids, drused and raphid crystals.
The diverse morphological features in flowers and fruits, especially in inflorescences, petals and stamens, provided valuable and reliable taxonomic characteristics. A detailed survey for flower and fruit parts (including the viviparous seedlings) were provided in this study. Some unique and curious phenomenon, including multi-cotyledons to united cotyledon and cotyledon collar, endosperm overflow, the present of coleorhiza in the hypocotyl of Bruguiera, provided interesting and valuable embryological information for the mangrove Rhizophoraceae. Downward and upward orientation seedlings on the mother trees were observed, however the latter were not noticed previously.
Two new taxa were recognized based on many lines of evidences in this study. A new species, Kandelia obovata C. R. Sheue, H. Y. Liu and J. W. H. Yong, which distributed northern from the South China Sea, was named and described. The detailed morphological and anatomical features of Ceriops australis (C. T. White) E. R. Ballment, T. J. Smith III & J. A. Stoddart were firstly described, which confirmed its taxonomic status. A systematic approach with a global view on the mangrove Rhizophoraceae is still needed, especially for Ceriops and Rhizophora.