Study on the Anatomical Structures of Rhododendron protistum var. giganteum with an Extremely Small Population
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摘要: 大树杜鹃(Rhododendron protistum var. giganteum)是杜鹃花科(Ericaceae)杜鹃属的常绿乔木,由于分布地域的局限性和资源的稀少性,该植物被列为我国首批极小种群野生植物保护名录.本文采用石蜡切片法和叶表皮装片法对大树杜鹃叶片、幼茎和根的解剖结构进行了研究,并利用扫描电镜对其种子表面纹饰、气孔以及叶毛被特征进行了观察.石蜡切片显微观察结果显示,大树杜鹃根的次生结构主要由周皮和维管柱组成,茎的解剖结构由表皮、皮层、韧皮部、木质部和髓组成;大树杜鹃的叶为异面叶,上表皮具角质层,气孔器只分布于下表皮,气孔器类型为无规则型,叶脉具发达的维管束鞘延伸区.扫描电镜观察结果发现,大树杜鹃叶片毛被由两层不同类型的毛组成,即上面一层为海绵状绒毛,下面一层为短的薄片状绒毛;种子具翅,有明显的背腹面之分,背腹面纵纹明显.该研究结果为进一步探明大树杜鹃的生物学特征、确定其系统分类位置和探讨其生境适应性提供了科学依据.Abstract: Rhododendron protistum var.giganteum is an evergreen tree that belongs to subgenus Hymenanthes and subsection Grandia from the family Ericaceae.It is a highly endangered species in a small area in the southern part of Yunnan Province in China.This plant has been listed in the Conservation Program for Wild Plants with Extremely Small Populations in China (2012-2015 Operational Plan) due to its limited distribution and small populations.In the present study, the anatomical characteristics of the leaves, stems and roots of R.protistum var.giganteum were studied by paraffin sectioning and leaf epidermal isolation.Furthermore, seed surface, stoma and indumentum characteristics were also observed under scanning electron microscope (SEM).The paraffin sectioning results indicated that the secondary structure of the root was mainly composed of periderm and vascular cylinder.The anatomical structure of the stem consisted of the epidermis, cortex, phloem, xylem and pith.The leaf was bifacial with a cuticle on the upper epidermis.The epidermal hairs and stomata were only distributed on the lower epidermis.The stomata were anomocytic type.Palisade tissue was arranged closely and was well-developed, while the spongy tissue was arranged loosely.There were well-developed vascular bundles and bundle sheath extensions distributed in the structure of the leaf.Through SEM, it was found that the foliar trichome of R.protistum var. giganteum was composed of two layers of epidermal hairs, including a layer of cavernous villi and a layer of short lamelliform villi.Basal and apical wings were equally developed on the seeds.Seeds were flattened and exotesta longitudinal sculptures, which were conformed on the dorsal and ventral sides of the seed.The results obtained in the present study will not only help to further understand the biological characteristics of this species, but also provide a scientific basis to elucidate its systematic classification and habitat adaptation.
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Keywords:
- Rhododendron /
- Classification /
- Anatomical structure /
- Adaptation /
- Epidermal hair /
- Endangered plant
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