Prenner Gerhard
Institute of Botany, Karl-Franzens-University Graz, Holteigasse 6, A-8010 Graz, Austria.
Ann Bot. 2004 May;93(5):537-45. doi: 10.1093/aob/mch076. Epub 2004 Mar 16.
The increase of molecular data and the resulting insights into legume systematics make the search for new morphological characters and a careful re-investigation of already stated characters necessary. Bracteoles are small, reduced leaves borne close to the base of lateral branches. Although they seem unimportant in older buds, they have an ecological function in protecting the sepal primordia. Furthermore, a morphogenetic function in mediating the onset of sepal initiation is suspected in the literature. The occurrence of bracteoles varies within Papilionoideae, and their distribution is used in legume systematics. But this is open to criticism, because there is a tendency to use 'absent' for 'caducous'. Thus attention here was paid to the initiation of bracteoles as well as to the sequence of sepal initiation.
The floral development of 30 taxa out of 15 tribes of Papilionoideae was investigated using scanning electron microscopy (SEM).
In five taxa the bracteoles initiated, but suppressed early. Furthermore, a broad variability of sepal initiation was found. Besides the widely stated unidirectional pattern, modified unidirectionality, tendencies towards whorled, fully whorled, bidirectional and successive initiation of sepals were all found.
Initiated but suppressed bracteoles are presented as a 'new' character in Papilionoideae. Considering the presence of bracteoles as a plesiomorphy, their suppression can be seen as a step towards completely reduced bracteoles. The remarkable variability of the sequence of sepal initiation questions the widely stated unidirectionality of organ initiation in Papilionoideae. The different modes of sepal initiation are deducible from the helical pattern of some caesalpinioids, which is seen as a developmental link of the flowers of Papilionoideae and Caesalpinioideae. The bidirectional sepal initiation is possibly a consequence of the morphogenetic function of bracteoles, although bidirectionality is not found in all taxa with reduced bracteoles.
分子数据的增加以及由此对豆科植物系统发育的深入了解，使得寻找新的形态特征以及对已描述特征进行仔细的重新研究成为必要。小苞片是着生于侧枝基部附近的小型退化叶片。尽管它们在较老的芽中看似不重要，但在保护萼片原基方面具有生态功能。此外，文献中怀疑其在介导萼片起始方面具有形态发生功能。小苞片的有无在蝶形花亚科中存在差异，其分布被用于豆科植物系统发育研究。但这受到批评，因为存在将“早落”用“无”来表示的倾向。因此，这里关注了小苞片的起始以及萼片起始的顺序。
利用扫描电子显微镜（SEM）研究了蝶形花亚科15个族中30个分类群的花发育情况。
在5个分类群中，小苞片起始，但早期受到抑制。此外，发现萼片起始存在广泛的变异性。除了广泛描述的单向模式外，还发现了改良的单向性、轮状、完全轮状、双向和连续起始萼片的倾向。
起始但受到抑制的小苞片被作为蝶形花亚科的一个“新”特征提出。考虑到小苞片的存在是一种原始特征，其抑制可被视为向完全退化小苞片发展的一步。萼片起始顺序的显著变异性对蝶形花亚科中广泛描述的器官起始单向性提出了质疑。萼片起始的不同模式可从一些云实亚科植物的螺旋模式推导出来，这被视为蝶形花亚科和云实亚科花的发育联系。双向萼片起始可能是小苞片形态发生功能的结果，尽管并非所有小苞片退化的分类群中都存在双向性。
