山茶科花粉超微结构及其系统学意义

POLLEN ULTRASTRUCTURE OF THEACEAE AND ITS SYSTEMATIC SIGNIFICANCE

借助光学显微镜、扫描电镜及透射电镜对分布于亚洲、北美洲及中南美洲山茶科１７属约５０种植物的花粉进行了系统的观察研究。本科花粉为３孔沟或３（拟）孔沟，近扁球形至近球形，少数近长球形。大小从１３～５０μｍ（极轴）×１３～５５．３μｍ（赤道轴）。表面纹饰可分为皱波状（或皱块状）、颗粒状、疣状、钝刺状、网状、穴网状及近乎光滑等类型。在皱波状纹饰中，其皱脊的组成分子又可分为颗粒、念珠状结构。外壁为具复盖－柱状层结构（ｔｅｃｔａｔｅ－ｃｏｌｕｍｅｌａｔｅ），复盖层－穿孔（ｔｅｃｔａｔｅ－ｐｅｒｆｏｒａｔｅ）或不穿孔（ｔｅｃｔａｔｅ－ｉｍｐｅｒｆｏｒａｔｅ）。其复盖层、柱状层、基层及外壁内层层次分明，但各层次的厚度及比例随不同属种而异。孢粉学资料完全支持把山茶科划分为两个亚科即山茶亚科（Ｔｈｅｏｉｄｅａｅ）及厚皮香亚科（Ｔｅｒｎｓｔｒｏｅｍｉｏｉｄｅａｅ）。其区别表现在花粉大小和外壁纹饰两方面。山茶亚科花粉最长轴直径从２５～５５μｍ，并且以３５～４５μｍ为常见；外壁纹饰多种多样；外壁结构为复盖层－穿孔，极个别为不穿孔（圆仔荷属Ａｐｔｅｒｏｓｐｅｒｍａ）。后一亚科花粉大小为１３～２０μｍ，多为１５～１８μｍ，外壁纹饰很微弱?

The pollen of 50 or so species representing 17 genera of Theaceae was examined by light microscope, scanning electron microscope and transmission electron microscope for the purpose to elucidate the systematic relationshipes of the family. The examination indicates that the pollen grains are 3-colporate basically,suboblate to spheroidal and a few to subprolate in shape, with size from 13～50 μm(polar axis) × 13～55 μm(equatorial axis). The pollen sculpture can be divided into rugulate, granulate, reticulate, foveolate, spinulate, verrucate and psilate types etc. The exine consists of tectum, columellae, foot layer and endexine. The thickness of exine and the ratios of tectum to columellae and extexine to endexine are more or less different in different genera. Pollen morphology supports to divide the family into two subfamilies, i.e.Theoideae and Ternstroemioideae,the former's pollen grains are medium-sized, with diameter from 25～55 μm, the sculpture can be divided into rugulate, granulate, reticulate, verrucate and spinulate or papillate types, but rugulate and reticulate types are two ordinary ones. In the latter, the pollen grains are small, with polar diameter from 13～20 μm, the surface of the pollen grains is nearly smooth, only a few foveae can be seen in parts of the surface. Therefore the two subfamilies can be recognized easily by the pollen size and sculpture. The pollen morphology indicates that the genera Pyrenaria and Parapyrenaria are indistinctive each other both in pollen size and sculpture, which supports to merge Parapyenaria into Pyrenaria. In addition, the systematic relationships among Gordonia, Polyspora, Laplacea and Apterosperma are discussed. Pollen morphological data support to merge the genus Polyspora into Gordonia. At last, from the comparison of pollen grains among different genera within Theaceae, an evolutionary trend of pollen morphology of Theaceae was summarized as follows: (1) size: from medium to small; (2) shape: from oblate→suboblate→subspheroidal→spheroidal; (3) sculpture: from rugulate→reticulate→foveolate→psilate. Based on the evolutionary trend of pollen morphology and incorporated with fossil data of Theaceae, we suggest that there are two main branches in the evolution of Theaceae, one is from Camellia→Pyrenaria(including Parapyrenaria) and Tutcheria; the second from Gordonia→Schima→Hartia, Stewartia and Apterosperma, and possibly from Stewartia or Hartia→Ternstroemioideae, or from Pyrenaria to Ternstroemioideae.