Taiwania

Floral development in Biancaea decapetala and Albizia julibrissin (Fabaceae: Caesalpinioideae), and its systematic significance This study investigates the floral morphology and development of two legume species from the subfamily Caesalpinioideae, Biancaea decapetala (a caesalpinioid), and Albizia julibrissin (a mimosoid), using scanning electron microscopy. The floral organ initiation in A. julibrissin involved the helical orientation of sepals’ formation, simultaneous initiation of petals, and formation of the ring meristem in place of stamens. Whereas in B. decapetala, organ whorls grow unidirectionally, from abaxial to adaxial, a characteristic found in the subfamily Papilionoideae. However, the floral development sequence in B. decapetala differs from papilionaceous flowers, as it lacks petal specialization and features a fused staminal tube. While fused sepal tube, free stamens, and short style were observed in flowers of B. decapetala; fused petals, fused staminal tube, and long style occurred in flowers of A. julibrissin. The petal aestivation is valvate in A. julibrissin, compared to ascending cochleate in B. decapetala. The observations during the initiation and developmental stages of floral whorls are essential to unravel the functional specificity of appendages. A. julibrissin belongs to the Mimosoid clade, which was until recently placed outside the Caesalpinioideae subfamily (of which B. decapetala was always been a part of) due to its floral architecture. There has been significant number of discussions and deliberations in the botanical community about the placement of this clade in the subfamily. Understanding of floral development in the subfamily and comparison of caesalpinioids with mimosoids can be crucial in evaluating the phylogenetic placement of the mimosoid clade. While most changes in the developmental sequence may appear subtle and minute, these are imperative for the remarkable disparity in the floral morphology of legumes.

本研究对豆科Caesalpinioideae亚科下的两种豆类植物，即Biancaea decapetala（金合欢科植物）和Albizzia julibrissin（含羞草科植物）的花部形态与发育进行了探讨。通过扫描电子显微镜技术，观察了A. julibrissin中花瓣原基的螺旋排列、花瓣的同步起始以及代替雄蕊的环状原基的形成。而在B. decapetala中，花器官轮生呈单向生长，从腹面至背面，这一特征在Papilionoideae亚科中可见。然而，B. decapetala的花部发育序列与蝶形花科不同，缺乏花瓣的专门化，并具有合生的雄蕊管。在B. decapetala的花朵中观察到合生的萼筒、游离的雄蕊和短柱头；而在A. julibrissin的花朵中则观察到合生的花瓣、合生的雄蕊管和长柱头。与B. decapetala的花瓣螺旋状排列相比，A. julibrissin的花瓣排列为瓣状。在花器官的原基起始和发育阶段进行的观察，对于揭示器官的功能特异性至关重要。A. julibrissin属于含羞草类群，此前因其花部结构而被置于Caesalpinioideae亚科之外（而B. decapetala则一直属于该亚科）。在植物学领域，关于此类群在亚科中的位置进行了大量的讨论和审议。对亚科下花部发育的理解，以及金合欢科与含羞草科的比较，对于评估含羞草类群的系统发育位置至关重要。尽管发育序列中的变化可能看似细微，但这些变化对于豆科植物的花部形态的显著差异是至关重要的。