Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Beijing 100093, People's Republic of China.
Am J Bot. 2004 Mar;91(3):361-8. doi: 10.3732/ajb.91.3.361.
The origin of the two envelopes of ovules of extant species of Ephedraceae has been discussed previously in different ways based only on investigation of bimerous female cones. To generalize the characteristics of the two envelopes, ontogenetic and metamorphic patterns of the two envelopes of ovules of trimerous female cones of Ephedra intermedia Schrenk et C. A. Meyer were studied using scanning electron microscopy. The outer envelope of the ovules of triovulate female cones of Ephedra intermedia is initiated as two adaxial lateral protuberances. Thus, the outer envelope of extant Ephedraceae may have been derived from three foliar components of the second proximal whorl of the secondary reproductive shoot of the ancestral compound female cone. Two adaxial lateral foliar components likely gave rise to the outer envelope by fusion, while the third abaxial foliar component was reduced. These new findings suggest that the Gnetales derived their female cones from trimerous multiaxial female reproductive organs of their progenitors. Some evolutionary aspects of female cones of Ephedra are also discussed.
以往有关麻黄科现存物种的双珠被胚珠起源的讨论，仅基于对双珠被雌球果的研究，提出了不同的观点。为了概括这两个珠被的特征，本研究利用扫描电子显微镜对中间麻黄三珠被雌球果胚珠的两个珠被的个体发生和变态模式进行了研究。中间麻黄三珠被雌球果的珠被外珠被是由两个近轴侧的侧生突起起始的。因此，现存麻黄科的外珠被可能是由次生复雌球果第二近轴轮生叶状器官的三个叶状组成部分衍生而来的。两个近轴侧叶状组成部分可能通过融合而产生外珠被，而第三个远轴侧叶状组成部分则退化。这些新发现表明，买麻藤类植物的雌球果起源于它们祖先的三珠被多轴雌性生殖器官。本文还讨论了麻黄属植物雌球果的一些进化方面。
