关键词：
ACHLOROPHYLLOUS ANGIOSPERMS
SAPROPHYTES
NONPHOTOSYNTHETIC ANGIOSPERMS
MYCO-HETEROTROPHY
MYCORRHIZA
摘要：
More than 400 species of vascular plants, in 87 genera, are achlorophyllous and heterotrophic, but not directly parasitic upon autotrophs. They are usually, but incorrectly, described as 'saprophytes' since they are in fact nourished by means of specialized mycorrhizal associations. Although distributed world-wide, they are most abundant and show the greatest species-richness in the Neotropics and Palaeotropical regions. Their aerial parts range in size from a few centimetres to extensive liane types up to 40 m long. With few exceptions, their habitats are dense moist forests in which there is a surface accumulation of leaf litter, often in situations which are too shaded for autotrophic growth. Although the achlorophyllous mycorrhizal mode of life has evolved independently many times and in widely disparate taxonomic groups, such plants show strong convergent evolution in particular adaptations to their peculiar mode of life. Most prominant amongst these are reductions in the size of seed and embryo, and the lack of differentiation of the embryo at maturity. The number of seeds produced by each flower is typically very large and the shape, structure and surface features of seeds involving adaptation for wind dispersal show remarkable parallels in many species. Specific adaptations for zoochory are rare but well developed in a small number of genera, some of which produce scents like fungal fruit bodies or floral parts which mimic fungal sporocarps. Vegetative parts are often even more conspicuously reduced. Most myco-heterotrophs are entirely subterranean for most of their lives and these stages exhibit adaptations consistent with a change in function from organs of absorption to organs of storage, shown by the almost universal loss of root hairs, decrease in surface area as exhibited in short cylindric 'vermiform' and tuberous roots or, in extreme cases, the complete suppression of roots and the formation of a swollen tuber or rhizome. Increased width of the root
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