Royal Botanic Garden, 20A Inverleith Row, Edinburgh EH3 5LR, Scotland, UK; and Institute of Cell and Molecular Biology, The University of Edinburgh, Edinburgh EH9 3JH, Scotland, UK.
Am J Bot. 2003 Dec;90(12):1696-707. doi: 10.3732/ajb.90.12.1696.
Titanotrichum oldhamii (a monotypic genus from Taiwan, Okinawa, and adjacent regions of China) has inflorescences bearing either showy yellow flowers or asexual bulbils. Asexual reproduction by bulbils is important in natural populations, and bulbil production increases in August and September at the end of the flowering season (which runs from June to the end of September). The bulbils are small (∼1-2.5 mm long) and numerous. They consist of a small portion of stem (bract-stem) topped by opposite storage bracts that enclose a minute apical meristem. A secondary root develops from the side of the bract-stem. The floral meristem of T. oldhamii has three possible fates: (1) bulbil formation, (2) flower formation, or (3) bracteose proliferation. Bracteose proliferation rarely occurs and appears to be a developmental transition between the bulbiliferous and racemose inflorescence forms. It is strongly reminiscent of the floricaula and squamosa mutants of Antirrhinum. In the bulbiliferous form a single floral primordium, which would normally produce one flower, gives rise to ∼50-70 bulbils by repeated subdivision of the meristem. This form of bulbil production appears to be unique to Titanotrichum. Occasionally a floral meristem divides, but the subdivision forms multiflowered units of up to four flowers rather than bulbils, suggesting that meristem fate is reversible up to the first or second meristem subdivision. In Titanotrichum, therefore, primordium fate is apparently not determined at inception but becomes irreversibly determined shortly after the appearance of developmental characteristics of the floral or bulbil pathway.
老岭苔草（一种单种属，来自台湾、冲绳及中国的邻近地区）的花序有两种类型，要么是鲜艳的黄花，要么是无性的珠芽。珠芽的无性繁殖在自然种群中很重要，并且珠芽的产生在八月份和九月份（花期从六月持续到九月底）增加。珠芽很小（约 1-2.5 毫米长）且数量众多。它们由一小部分茎（苞叶-茎）组成，顶部有一对相对的贮藏苞叶，苞叶内包含一个微小的顶端分生组织。次生根从苞叶-茎的侧面发育而来。老岭苔草的花分生组织有三种可能的命运：（1）珠芽形成，（2）花形成，或（3）苞片状增殖。苞片状增殖很少发生，似乎是珠芽状和总状花序形式之间的发育过渡。它强烈地让人想起金鱼草的花被片和鳞片突变体。在珠芽状形式中，一个原本会产生一朵花的单个花分生组织通过多次分生组织的细分，产生约 50-70 个珠芽。这种形式的珠芽产生似乎是老岭苔草所特有的。偶尔，花分生组织会分裂，但细分形成的是多达四朵花的多花单位，而不是珠芽，这表明分生组织的命运在第一次或第二次分生组织细分之前是可逆的。因此，在老岭苔草中，原基的命运显然不是在起始时就确定的，而是在花分生组织或珠芽分生组织途径的发育特征出现后不久就确定的。
