Tokuoka Toru, Tobe Hiroshi
Department of Natural Environmental Sciences, Faculty of Integrated Human Studies, Kyoto University, Kyoto 606-8501, Japan.
J Plant Res. 2003 Oct;116(5):355-80. doi: 10.1007/s10265-003-0116-4. Epub 2003 Aug 29.
Acalyphoideae, the largest subfamily of Euphorbiaceae, are investigated with respect to ovule and seed structure on the basis of 172 species of 80 genera in all 20 tribes of Acalyphoideae sensu Webster. All species of Acalyphoideae examined have bitegmic ovules with a non-vascularized inner integument. However, noticeable differences exist among and sometimes within the genera in the thickness of the inner and outer integument, the presence or absence of vascular bundles in the outer integument, whether ovules are pachychalazal or not, the presence or absence of an aril, seed coat structure (in terms of the best-developed mechanical cell-layer), and the shape of cells constituting the exotegmen. For the latter two characters, two different types of seed coat (i.e., "exotegmic" and "exotestal") and three different types of exotegmic cell (i.e., palisadal, tracheoidal and ribbon-like) were distinguished. Comparisons showed that three tribes Clutieae, Chaetocarpeae and Pereae are distinct from the other Acalyphoideae as well as from the other Euphorbiaceae in having an exotestal seed coat with a tracheoidal exotegmen. The tribe Dicoelieae is also distinct from the other Acalyphoideae in having an exotegmic seed that is composed of ribbon-like cells of exotegmen (i.e., cells both longitudinally and radially elongated, sclerotic and pitted). The tribe Galearieae, which should be treated as a distinct family Pandaceae, is also distinct from the other Acalyphoideae in having an exotegmic seed with a tracheoidal exotegmen (i.e., cells longitudinally elongated, sclerotic and pitted). The remaining genera of Acalyphoideae always have an exotegmic seed with a palisadal exotegmen (i.e., cells radially elongated, sclerotic and pitted). The shared palisadal exotegmen supports the close affinity of Acalyphoideae (excluding five tribes) with Crotonoideae and Euphorbioideae. Within the remaining genera of Acalyphoideae, a significant diversity is found in ovule and seed morphology with respect to the thickness of the inner and outer integument, the size of chalaza, vascularization of an outer integument and an aril.
叶下珠亚科是大戟科最大的亚科，本文基于Webster系统下叶下珠亚科所有20个族中80属的172个物种，对其胚珠和种子结构进行了研究。所有被研究的叶下珠亚科物种都具有双珠被胚珠，其内珠被无维管束。然而，各属之间甚至同一属内的不同物种，在内珠被和外珠被的厚度、外珠被中维管束的有无、胚珠是否具厚珠脐、假种皮的有无、种皮结构（以发育最好的机械细胞层而言）以及构成外种皮的细胞形状等方面存在显著差异。对于后两个特征，区分出了两种不同类型的种皮（即“外种皮型”和“外种被型”）以及三种不同类型的外种皮细胞（即栅栏状、管状和带状）。比较结果表明，Clutieae、Chaetocarpeae和Pereae这三个族与其他叶下珠亚科以及其他大戟科植物不同，它们具有外种被型种皮，其外种皮为管状细胞。Dicoelieae族也与其他叶下珠亚科不同之处在于，它具有由外种皮的带状细胞组成的外种皮型种子（即细胞在纵向和径向上都伸长，硬化且具小孔）。Galearieae族应被视为一个独立的科——小盘木科，它也与其他叶下珠亚科不同，其外种皮型种子的外种皮为管状细胞（即细胞纵向伸长，硬化且具小孔）。叶下珠亚科的其余属总是具有外种皮型种子，其外种皮为栅栏状细胞（即细胞径向伸长，硬化且具小孔）。共有的栅栏状外种皮支持了叶下珠亚科（不包括五个族）与巴豆亚科和大戟亚科的密切亲缘关系。在叶下珠亚科的其余属中，在胚珠和种子形态方面，在内珠被和外珠被的厚度、合点大小、外珠被的维管束化以及假种皮等方面发现了显著的多样性。
