梧桐科翅子树属的亲缘关系

ON THE AFFINITIES OF PTEROSPERMUM SCHREB. (STERCULIACEAE)

翅子树属传统上均作为梧桐科山芝麻族的成员,但也有少数人将它归到Dombeyeae族中。本文根据对翅子树属的外部形态及花粉形态特征的研究,并结合其解剖、染色体和胚胎发育的资料,对翅子树属的亲缘关系进行了分析。翅子树属与山芝麻族在外部形态上比较接近,但在解剖、花粉形态和染色体基数等特征上则差异显著;与Dombeyeae族在花粉形态上一致,但在外部形态(花结构)、染色体基数和瓦形细胞等特征方面则明显不同,反映了翅子树属在这两个族之间的过渡状态,不宜作为任何一族的成员,应该作为一个独立的族存在,其在梧桐科中的位置在Dombeyeae附近。

The genus Pterospermum Schreb. is traditionally placed in the Helic-tereae, occasionally in the Dombeyeae. The affinities of this genus are discussed based on the morphological and palynological studies, together with the data from the grounds of anatomy, cytology arid embryology. Morphologically it resembles the Helictereae to some extent but differs from this tribe in the structre of and-roecium and from the Dombeyeae in the structure of flowers. In wood anatomy, Pterospermum differs from the Helictereae in pore multiples of 2 or 3 cells, pores 1-5 per sq mm. and from the Dombeyeae in the presence of tile cells (Pterospermum type). The basic chromosome number of Pterospermum, x=19, is different from that of Helicteres, x=9, and that of Kleinhovia x=10. Its basic chromosome number is also disaccordant with the main basic chromosome number in the Dombeyeae, x=10, though it is the same as that of Pentapetes. The pollen grains of Pterospermum, which are spheroidal, amb circular, 3-porate, exine spiny, recall those of the Dombeyeae but differ from those of the Helictereae, which are 3-porate or 3-3-colporate, amb triangular or subcircular, exine reticulate. In embryology, a number of features are common to Pterospermum and other Sterculiaceaa, and showing more similarities to the Dombeyeae than to the Helictereae. But the secondary increase in sporogenous tissue, the thin-walled nutrient tissue under mul-ticelled megaspore archesporium, the functioning of subhypodermal archesporium cells, the development of double and triple embryosacs in an ovule, are disagreed with the Helictereae, the Dombeyeae and other taxa of the Sterculiaceaa, indicating the rather isolated position of Pterospermum. It seems unreasonable to place Pterospermum in either the Helictereae or the Dombeyeae. A new tribe, Pterosper-meae, therefore, is established for this genus. The new tribe is placed close to the Dombeyeae.