Phylogenetic and evolutionary studies of rheophytes in the everwet tropics

1.从Bomeo采集或记录的蕨类风生植物约60种，比1981年记录的Van Steenis记录的12种多得多，接近82种被子植物。这表明婆罗洲蕨类风生植物的多样性比目前所了解的要大得多。风生苔藓植物的特征是：叶多层；茎坚韧，经常爬行；植株矮小；茎分枝合生，植株垫状。在这些性状上，风生苔藓植物(配子体)与维管风生植物的孢子体相似，而不是与配子体相似。热带风生植物和相关旱地植物的比较叶解剖研究表明，风生植物狭叶的部分原因是叶肉细胞较少扩张，叶肉细胞臂较短，细胞间隙比旱地植物的宽叶小。风生植物及其相关旱地物种的叶片发育研究，以考察风生植物的狭窄叶是如何在个体发育过程中形成的。在…在早期，流变性狭窄叶的原基比旱地阔叶的原基小。在细胞扩张阶段，狭窄叶比旱地叶片更早停止扩张，这可能是由于异时性(早熟)所致。狭叶植物较小的细胞间隙导致较低的光合作用速率，这可能使风生植物难以在光合作用较活跃的旱地物种生长的陆地生境中生长。分子系统学研究表明，流变型紫草与陆生紫草(东亚)的亲缘关系比与陆生紫草(北美、欧洲等)的亲缘关系更近，尽管后两者在形态上相似。这一结果证实了风生植物来源于旱地植物。对流生紫草和陆生紫草配子体发育的研究表明，两种植物配子体形态无明显差异，但流生配子体生长较快，较早产生更多的孢子体，紫草采取世代适应策略。较少

1. About 60 species of fern rheophytes collected or recorded from Bomeo are much more than 12 species van Steenis recorded in 1981 and approach 82 angiosperm species recorded from there. It indicates much greater diversity of the fern rheophytes of Borneo than understood at present.2. Rheophytic bryophytes can be characterized as : leaves multi-layered ; stems tough, often creeping ; plants low in height ; stem-branching sympodial and plants matted. In these characters, rheophytic bryophytes (gametophytes) resemble the sporophytes of vascular rheophytes rather than the gametophytes.3. Comparative leaf anatomical study of tropical rheophytes and related dry-land species shows that rheophytic stenophylly is due partly to less expanded, short-armed mesophyll cells and consequent smaller-spaced intercellular spaces than broad leaves of dryland species.4. Leaf developmental study of a rheophyte and related dry-land species to examine how rheophytic stenophylls are formed during ontogeny. At … More an early stage the primordia of the rheophytic stenophylls are smaller than those of dry-land broad leaves. During the cell-expansion stage the stenophylls cease to expand earlier than the dry-land leaves, presumably due to heterochrony(paedomorphosis). Smaller intercellular spaces of the stenophyll result lower photosynthetic rate, which is assumed to make the rheophytes difficult to grow in terrestrial habitat in which photosynthetically more active dry-land species grow.5. Molecular systematic study shows that the rheophytic Osmunda lancea is more closely related to the terrestrial O. japonica (eastern Asia) than to the terrestrial O. regalls (North America, Europe etc.), although the last two morphologically resemble one another. The result confirms that the rheophyte is derived from the dry-land species.6. Developmental study of gametophytes of the rheophytic Osmunda lancea and the terrestrial O. japonica shows that there is no marked difference in gametophyte morphology but the rheophytic gametophytes grow faster to produce more sporophytes earlier than the dry-land ones, and that O. lancea takes generation-specific adaptive strategy. Less