Evolution of life forms and mycorrhizal relationships in Cymbidium

兰花西南。一种兰花属，分布于。东亚及东南亚至澳洲，共有约50种。该属具有独特的生态多样性，存在于陆生、附生和岩生的生命形式中。此外，大花蕙兰部分缺乏叶片，具有专性的真菌营养存在。本文对大花蕙兰及其姊妹科大多数种的各种形态解剖特征与生态学性状进行了相关性研究。此外，还使用了大花蕙兰的分子系统发育树（Yukawa et al.2002）来检查这些性状的系统发育约束。结果表明：(1)在大花蕙兰中，石生和陆生生命形式至少有三次可能从附生生境演化而来。(2)专性真菌营养谱系，蕙兰科厚根属从陆生祖先分化而来。(3)附生植物的种子比陆生植物的种子含水量更高、体积更大。(4)专性真菌营养物种的种子大小比其姐妹光合物种大得多。(5)枝状根状茎只在陆生植物中发育。我们发现这种类型的根茎是菌根真菌的主要住所。(6)叶厚壁组织纤维的发育与附生程度有关。(7)栅栏组织和amphistom气孔的分化可能是适应强光胁迫的结果，因为具有这些特征的物种栖息在暴露位置的树木上。(8)在蕙兰根和/或根状茎中发现了兰花型内生菌根真菌和树外生菌根真菌。尽管陆生蕙兰与这两种真菌都有共生关系，但附生蕙兰只与兰花型内生菌根真菌有共生关系。另一方面，专性真菌种类只与树外菌根真菌共生。少

Cymbidium Sw., an orchid genus distributed from. East and Southeast Asia to Australia, comprises about 50 species. The genus exhibits distinctive ecological diversification and occurs in terrestrial, epiphytic, and lithophytic life forms. Moreover, Cymbidium section Pachirhizanthe lacks foliage leaves and has an obligate mycotrophic nutritional existence. In this study correlation between various morphological and anatomical characters and ecological characters was tested for most species of Cymbidium and its sister groups. Furthermore, a molecular phylogenetic tree of Cymbidium (Yukawa et al.2002) was used to examine phylogenetic constraint of these characters. The following insights were provided : (1)In Cymbidium, lithophytic and terrestrial life forms were likely to be derived from epiphytic habitat at least three times. (2)The obligate mycotrophic lineage, Cymbidium section Pachyrhizanthe diverged from a terrestrial progenitor. (3)The seed of epiphytic species showed higher hydrop … More hilicity and larger dimensions than that of terrestrial species. (4)The seed size of obligate mycotrophic species decreased greatly in comparison with its sister photosynthetic species. (5)Development of ramified rhizomes was found only in terrestrial species. We found that this type of the rhizome is the principal dwelling for mycorrhizal fungi. (6)In this genus, development of sclerenchymatous fibers in leaves is correlated to the degree of epiphytism. (7)Differentiation of palisade tissue and amphistomaty are likely adapted to high light stress because the species possessing these characters inhabit trees at exposed positions. (8)Orchid-type endomycorrhizal fungi and tree ectomycorrhizal fungi were found in Cymbidium roots and/or rhizomes. Although terrestrial Cymbidium species symbiose with both types of fungi, epiphytic species show symbiosis only with Orchid-type endomycorrhizal fungi. On the other hand, obligate mycotrophic species symbiose exclusively with tree ectomycorrhizal fungi. Less