| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 104 === Rhizophoraceae are diversified both ecologically and morphologically and subdivided into three tribes: tribe Rhizophoreae, tribe Gynotrocheae, and tribe Macarisieae. Tribe Rhizophoreae is exclusively recognized as mangrove species widely distributed in the intertidal areas along pantropical coastlines; but Gynotrocheae (mainly in Asia and South America) and Macarisieae tribes (mainly in Africa) are inland species distributed in pantropical moist forests. Leaves are the dominant plant organ exposed to the environment. Mangrove and inland species live in such different habitats that their leaves may have different adaptations to their environments. The aim of this study is to compare the differences in leaf morphological and anatomical characteristics between the mangrove and inland species of Rhizophoraceae. Ten genera with 26 species sampled from three tribes of Rhizophoraceae were collected in the field and herbaria for this study. In addition, special features in the structure and development of cork warts of mangrove Rhizophora stylosa were explored with a view to understanding their ecophysiological functioning.
The results show significant major differences in leaf morphological and anatomical characteristics between mangrove and inland species. All the taxa of mangrove Rhizophoraceae have thick, coriaceous and entire leaves without trichomes but with relatively large stomata low in density. The leaves of mangrove species are covered with a thick cuticle, with one to multiple-layered well-developed hypodermal cells adjacent to epidermal cells, enlarged terminal tracheids and sunken cyclocytic stomata connected with distinctive inner and outer cuticular ridges. The genus Rhizophora has the most complicated leaf structures in the mangrove Rhizophoraceae, with highly-developed hypodermis, additional funnel-shaped mucus cells, four types of idioblasts and regular cork warts. Excepting the epidermal tissue, druse form crystals were found in the leaf tissues of mangrove Rhizophoraceae.
However, the inland species of the two tribes have thin leaves usually covered with trichomes, entire or toothed, with small stomata in high density. The leaf structure of inland species of Rhizophoraceae is similar to general plants, consisting of epidermis, palisade and spongy tissues, but may differ by having mucus cells mingled with the adaxial epidermal cells. The stomata of the inland Rhizophoraceae are not sunken, but including more diverse types than the mangrove species, including anomocytic, anisocytic and brachyparacytic stomata. Most of the taxa only have small and inconspicuous outer stomatal cuticular ridges. The inland species also have more diverse crystal types than mangrove taxa including druses, raphides, and prismatic crystals in the mesophyll and epidermis.
Black dot-like cork warts were commonly found on the abaxial leaf surface in Rhizophoraceae. Two types of cork warts are recognized in this study: (1) stomata-type: found in several mangrove and inland species; (2) trichome scar: only found in Pellacalyx. Stomata-type cork warts of R. stylosa develop from the earliest originating stomatal complex on the leaf primordium which is still ensheathed inside the stipule. The cells adjacent to the stoma undergo anticlinal and periclinal divisions, and finally form the spherical structure of a cork wart. Cork warts gradually turn dark during development. A mature cork wart shows peripheral cells surrounding core cells filled with solid substances in a transverse view. Abundant tannins are present in an entire cork wart, however, lignin occurs only on the cell walls of the core cells. Tannins are abundant in cork wart cells; cell walls in the core cells of the cork wart are lignified. The salt elements (Na, K, Cl, Mg) gradually accumulate on the surface of cork warts during leaf development and ageing, but not in the core cells of cork warts.
This comparative study first reveals a strong correlation between leaf structures and the adaptation to the environments of Rhizophoraceae. The leaves of mangrove taxa are characterized with xeromorphic anatomical traits: thick cuticle, hypodermis, idioblasts, enlarged terminal tracheids, and distinctive stomatal cuticular ridges. Based on the characters of stomatal types, trichomes and leaf structure, tribe Macarisieae is more primitive and the mangrove tribe Rhizophoreae is more derived. The cork warts of mangrove Rhizophora are proved to originate from stomata complexes formed at a very early stage, with potential roles for substance storage and salt accumulation.
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