安息香科的系统位置及地理分布

安息香科为柿目的一成员，包括１１个属，为一自然的分类群．它与山茶科很接近，并可能是从它的祖先类群演化而来的．本文分析其形态特征的演化趋势，认为子房上位，花冠裂片覆瓦状排列，雄蕊为花冠裂片两倍，花序圆锥花序为原始性状，而子房下位．花冠裂片镊合状排列，雄蕊与花冠裂片的同数，花序少花或单花为进化性状．安息香属为本科最大的属，形态变异多样化，既具有最原始性状，为本科原始类群代表，同时又有较多进化性状．其他各属可能是以它作为基干演化而来．从分析各属的分布区类型，本科有７属分布于热带地区，但仅有３属真正分布于热带，其余４属分布于亚热带或其边缘地区．因此，安息香科基本上是一个热带科，但不典型，它可能是从古热带山区的亚热带地区演化而来的．根据全科的属和种的统计，有１１属，１５０余种，间断分布于欧亚和美洲两大陆块上，亚洲有１０属，５７种，主要分布于东亚，在这一地区，以我国秦岭和长江以南至南岭以北及华西南种类最丰富，包括有最原始类群和系统演化各阶段类群；热带南美洲有２属８３种，这一带种类虽丰富，但仅２属及缺乏原始类群．因此，我们称东亚为安息香科的分布和分化中心，而热带南美洲为第二分布中心．根据化石记载结合本科现代分布格局，我们

SYSTEMATIC POSITION AND GEOGRAPHICALDISTRIBUTION OF STYRACACEAE

The systematic position, evolutionary trends, modem distribution pattern, center ofdistribution and differentiation of Styracaceae are discussed. Styracaceae, comprising 11 genera, is a natural group in the Ebenales. Embryological and morphological evidences indicatethat it was most fibly evolved from Theaceae. Morphologically, the superior ovary, imbricatecorolla-lobes, stamens twice as many as corolla-lobes and inflorescences paniculate areconsidered as primitive features, while the inferior ovary, valvate corolla-lobes, stamens asmany as corolla-lobes and inflorescences with fascicled or solitary nowers, advanced features. In Styracaceae, Styrax is the largest and most diverse genus with both primitive andadvanced features. The other genera are closely ailled and seem to have a common originfrom tile Styrax stock.Floristically, six distribution patterns of the eleven genera are recognized. 1. Pantropic:Styrax, 2. Tropical Asia f Rehderodendron,Huodendron, Alniphyllum, Parastyrax, Bruinsmia,3. E. Asia and N. America disjunct:Halesia. 4. E. Asia: Pterostyrax, 5. Endemic to China: Sinojackia,Melliodendron,6.Tropical America f Pamphilia. Among the seven genera distributed to tropical areas only three actually occur in tropical regions,the others are insubtropical regions or on the fringe of it. Therefore, Styracaceae may be considered asmainly but not typically a tropical family,and originated from tropical mountains in thepast.The floristic analysis shows that there are 10 genera and 57 species(8 endemic genera,34 endemic species)in East Asia,occupying 91% and 36% of the total genera and speciesin this family respecitively.Ther are 10 genera and 54 species in China,mostly in areasfrom Qinling Mountains and Changjiang river to Naming Mountains,and S.W.China,including most primitive group (Styrax series Imbricatae)and the group of variousevolutionary stages.In tropical America there are two genera,83 species(1 endemic genera,76 endemic species),occupying 18% and 52% of the total genera and species of this familyrespectively.Although, tropical America is most rich in species, but there are only two generaand lack of primitive group. For this reason,East Asia is considered as a primary centerof the distribution of Styracaceae species,and tropical America, secondary center.According to the fossil record and modern distribution pattern of Styracaceae, the ancestor of this family maybe originated in Cathaysia flora during the Cretaceous time.