Rudall Paula J, Bateman Richard M, Fay Michael F, Eastman Alison
Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK;
Am J Bot. 2002 Dec;89(12):1867-83. doi: 10.3732/ajb.89.12.1867.
The floral structure of Alliaceae is assessed in relation to the systematics of the family, especially the nature of the component parts of the remarkably insect-like flower of Gilliesia graminea. Both presence of solid styles and possession of tenuinucellate ovules represent consistent synapomorphies for Alliaceae and support the separation of Agapanthus and Themidaceae from Alliaceae. Within Alliaceae, absence of septal nectaries (i.e., complete fusion of carpel margins) is a synapomorphy for the sister genera Gilliesia and Gethyum; septal nectaries are present in all other Alliaceae. A gynobasic style and reduced ovule number are probable synapomorphies for the genus Allium. In contrast to most other Alliaceae, in Gethyum and Gilliesia only three (abaxial) stamens (A1, a1, a2) are expressed, as in the apostasioid orchid Neuwiedia, but the perianth of Gethyum is only slightly bilaterally symmetric (zygomorphic), whereas Gilliesia graminea shows bilateral symmetry in all three floral whorls: perianth (suppression of the inner adaxial tepal in most flowers), androecium (suppression of three adaxial stamens), and gynoecium (slight bilateral symmetry, evident in transverse section). The precise relationships of Miersia and Solaria, the other two genera of Alliaceae with bilaterally symmetric flowers, are unknown, but their morphology indicates a close relationship with Gilliesia and Gethyum. Appendages of tepaline origin occur in Gethyum, Gilliesia, and Miersia; their papillate epidermis suggests that they function as osmophores. Their presence in Miersia, which has six stamens, indicates that these novel structures, which develop late in floral ontogeny, evolved independently from stamen suppression in this group. Within Gilliesia graminea, the genetic mechanisms controlling tepal number and shape are apparently unstable, resulting in fluctuating asymmetry. In G. graminea the possession of insect mimicry, presence of osmophores and absence of nectar together indicate a deceitful pollination mechanism similar to that of some Orchidaceae; this would make Gilliesia highly unusual among non-orchid monocots, given that pollination by sexual deceit is normally regarded as exclusive to orchids.
针对葱科的系统分类，尤其是细叶吉氏葱（Gilliesia graminea）那显著类似昆虫的花朵各组成部分的性质，对葱科的花部结构进行了评估。实心花柱的存在以及具薄珠心胚珠均是葱科一致的共衍征，支持将百子莲属（Agapanthus）和仙茅科（Themidaceae）从葱科中分离出来。在葱科内部，隔膜蜜腺的缺失（即心皮边缘完全融合）是姐妹属吉氏葱属（Gilliesia）和盖氏葱属（Gethyum）的共衍征；其他所有葱科植物均有隔膜蜜腺。雌蕊基生花柱和减少的胚珠数可能是葱属（Allium）的共衍征。与大多数其他葱科植物不同，在盖氏葱属和吉氏葱属中，仅表达三个（远轴）雄蕊（A1、a1、a2），如同无叶兰亚族（apostasioid）的兰花纽氏无叶兰（Neuwiedia），但盖氏葱的花被仅略微两侧对称（两侧对称），而细叶吉氏葱在所有三个花轮中均表现出两侧对称：花被（大多数花朵中内轮近轴花被片的抑制）、雄蕊群（三个近轴雄蕊的抑制）和雌蕊群（轻微两侧对称，在横切面上明显）。葱科另外两个具两侧对称花朵的属——米尔氏葱属（Miersia）和索拉氏葱属（Solaria）的确切关系尚不清楚，但它们的形态表明与吉氏葱属和盖氏葱属关系密切。盖氏葱属、吉氏葱属和米尔氏葱属中存在花被片起源的附属物；其具乳头状表皮表明它们起到发香器官的作用。它们在具六个雄蕊的米尔氏葱属中的存在表明，这些在花发育后期形成的新结构是在该类群中独立于雄蕊抑制而进化的。在细叶吉氏葱中，控制花被片数量和形状的遗传机制显然不稳定，导致波动不对称。在细叶吉氏葱中，具有昆虫拟态、发香器官的存在以及花蜜的缺失共同表明一种类似于某些兰科植物的欺骗性传粉机制；鉴于性欺骗传粉通常被认为是兰花所特有的，这将使吉氏葱属在非兰科单子叶植物中极为特殊。
