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Pollen Morphology and Its Systematic Significance in the Ericaceae

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タイトル: Pollen Morphology and Its Systematic Significance in the Ericaceae
その他のタイトル: ツツジ科植物の花粉形態とその体系学的意義
著者: Sawara, A.K.M. Golam 著作を一覧する
発行日: 2007年 3月
抄録: A detailed description of the range of pollen morphological variation within the family Ericaceae sensu Kron et al. (2002a) has been presented. For this palynological investigation, 275 taxa of 270 species representing 57 genera and 6 subfamilies were studied with light (LM) and scanning electron microscopy (SEM), and 31 species with transmission electron microscopy (TEM). The systematic significance and evolutionary trends of palynological characters have been discussed in the light of the recent phylogenetic classification of the Ericaceae. Pollen grains are dispersed as monads, tetrads or polyads, commonly of medium (30 – 50 µm) size and 3-colpor(oid)ate. Viscin threads are present only in a few genera of the subfamily Ericoideae (Bejaria and other eight genera). With SEM, exine sculpture varies from finely verrucate to psilate, and twelve major exine sculptural types have been recognized. Two dichotomous keys to the pollen of Ericaceae were prepared with the characters observed under LM, and exine sculpture with SEM. With TEM, the exine structure of ericaceous pollen is basically the same, and composed of sexine; tectum and columellae and nexine; foot layer and endexine. Two unique exine structures, granular columellae and canalized tectum, were observed in the monad pollen of two Erica species, E. barbigera and E. recurvifolia, and the tectum with (a few) canals also observed in Rhododendron japonicum and Oxydendrum arboreum. The TEM observations were also found useful to confirm some critical palynological observations with LM and/or SEM: heterodynamosporus tetrads, different types of exine sculpture, tetrads without septa, presence of pollenkitt and pollenkitt ropes, cause of pollen shrinkage, and identification and realignment of taxa. The family Ericaceae is eurypalynous enough to clarify the differentiation of species and genera, but has limited potential for clarification of the demarcation and relationships of higher taxa (e.g., tribes). Generally, the recent classifications and relationships among the vgenera of Ericaceae were supported by results of the present study. Qualitative palynological characters (e.g., exine sculpture) were found to be taxonomically more important than quantitative characters (e.g., tetrad diameter), and various palynological characters important for different taxonomic levels. Palynological features were also found to be significant in some infrageneric classifications (e.g., Arctostaphylos), and to identify the monophyly of taxa (e.g., Dimorphanthera). Moreover, some taxonomic problems were presented, and realignments of some taxa have been suggested from the palynological view point, e.g. tribal limits of the tribe Bejarieae. Individual generic status of the following three taxa has been proposed: Erica recurvifolia E.G.H. Oliv. as Eremia recurvata Klotzsch; Rhododendron tsusiophyllum Sugim. as Tsusiophyllum tanakae Maxim.; and Vaccinium japonicum Miq. as Hugeria japonica (Miq.) Nakai. At least one misplaced species was also identified; Enkianthus sikokianus (Palibin) Ohwi should be recognized as a separate species, but it has been incorporated into E. campanulatus (Miq.) Nicholson. The present study revealed a number of evolutionary trends in different palynological features viz., pollen dispersal units, compactness of tetrads, pollen size and shape, aperture number and exine sculpture, within the family Ericaceae as well as within a genus (e.g., Enkianthus), and suggestions were made concerning the selective value of some of these trends. There is no clear correlation between pollen features of the family Ericaceae and either pollinators or geographical distributions, but present in lower taxa (e.g., Rhododendron, Erica). In the course of the pollen survey the following interesting discoveries were made: the first unique palynological feature – pollen tetrads without septa for the Ericaceae (e.g., Ceratostema) as well as other angiosperm families; the parallel evolution of pseudomonad pollen tetrad development in the subfamily Styphelioideae and Vaccinioideae; pollenkitt ropes were found on the dried herbarium specimens (e.g., Notopora); and pollen tetrads with four aperturate grains were discovered in a number of taxa (e.g., Vaccinium).
学位授与機関: Hokkaido University(北海道大学)
取得学位の種別: 博士
取得学位の分野: 農学
資料タイプ: theses (doctoral)
出現コレクション:博士 (農学)

提供者: Sarwar, A.K.M. Golam


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