从幼苗形态学特征探讨红豆杉科各属间的系统演化

本文根据幼苗的形态学特征，尤其是子叶的结构、说明在红豆杉科中最原始的属是榧树属，其幼苗为留土萌发，植株粗壮；子叶肥厚，有吸收功能，叶肉不分化，其细胞中充满淀粉粒：维管束在子叶的上部或顶部为单束2条，下部合并成双束1条。其次是穗花杉属，幼苗为出土萌发，植株粗壮，下胚轴的下部肥厚；子叶稍肉质，叶肉不分化，质体淡绿，有一定的光合功能，但主要是积累淀粉，维管束双束1条，在子叶的顶端趋于分裂。最进化的是红豆杉属和白豆杉属，可能还有澳洲红豆杉属，其幼苗为出土萌发，植株纤细；子叶薄，叶状，叶肉分化成栅栏和海绵组织，维管束单束1条。本科中族的划分和属的系统排列，从原始到进化，应该是：族1．榧树族(1．榧树属)；族2．穗花杉族(2．穗花杉属)；族3．红豆杉族(3．澳洲红豆杉属，4．红豆杉属，5．白豆杉属)。

ON PHYLOGENY OF THE TAXACEAE FROM MORPHOLOGY OF SEEDLINGS

This paper deals with the morphology of seedlings of the Taxaceae in China. Our morphological and anatomical investigations reaved that the cross morphology of seedings and the structure of the cotyledons can be used to explain the phylogeny of the Taxaceae, and the seedlings of the Taxaceae can be classified into three types. In Type I, represented by only Torreya, seedlings strong, hypogeal; hypocotyl very short; cotyledon thick and fleshy, with some stomata on the upper epidermis which is protective tissue, but with no stomata on the lower epidermis, which absorbes nutrient from endosperm; mesophyll has not differentiated into palisade and spongy parenchyma, and with abundant starch grains in its cells; two vascular bundles lie side by side in the upper part or at the top of the cotyledon, but fuse into one in the lower part of the cotyledon, and a resin canal present on the side of phloem. In Type I , represented only by Amentotaxus, seedling strong, epigeal; hypocotyl elongated and thickened in the lower part; cotyledon somewhat fleshy, with some stomata on the upper epidermis but no on the lower epidermis; mesophyll not differentiated into palisade and spongy parenchyma; plastid greenish, but accumulated starch mainly; vascular bundle single, wide and flat, but it tends to divide into two near the tip of the cotyledon resin canal absent. In Type II , represened by Taxus, Pseudotaxus, and probably, seedling thin, epigeal; hypocotyl elongated, slender (somewhat thick in the lower part in Austrotaxus only); cotyledon thin, leaf-like, Without stomata on the upper epidermis, but with stomata arranged in line, forming stoma band on the lower epidermis; mesophyll differentiated into palisade and spongy parenchyma and functions like a true leaf; vascular bundle single, narrow; resin canal absent. These three types represent a phylogenetical sequence from primitive to advanced.