天南星科Remusaia vivipara岩芋（臺灣目賊芋）和Remusaia pumila曲苞岩芋的無性珠芽發育和生殖策略的多樣化

Asexual Bulbil Development and Diversification of Reproductive Strategy between Remusatia vivipara and Remusatia pumila (Araceae)

岩芋（臺灣目賊芋）和曲苞岩芋能產生有性花和無性繁殖珠芽。然而岩芋很少產生種子，而曲苞岩芋卻是常見種子與珠芽。本文的研究目的是要了解無性繁殖的珠芽發育和岩芋有性生殖的問題。岩芋和曲苞岩芋的珠芽枝條均從塊莖的上部發育出來，而珠芽則簇生在珠芽枝條的節上。利用掃描式電子顯微鏡和光學顯微鏡的觀察結果顯示珠芽發育時，珠芽外附倒鉤鱗片，此鱗片的發育與葉子的發育順序及位置相似，各錯開約120°逐漸發出佈滿珠芽外側。鱗片能氈附動物皮毛，有助於珠芽向外傳播。花粉活性及花粉管萌發實驗的結果顯示曲苞岩芋的花粉具有活性，能產生花粉管，然而岩芋當小孢子母細胞分裂時，出現橋鏈的情況，使岩芋產生無活性的花粉，花粉管無法生長。進一步進行染色體的計數，確認岩芋為三倍體植物。就這兩種珠芽植物的生殖策略而言，岩芋完全依賴無性生殖，而曲苞岩芋則兼具有性生殖及無性生殖。然而珠芽枝條的發育是天南星科一個獨特的演化現象，這群植物也就是依據此特徵而歸類成為岩芋屬。

Remusatia vivipara and Remusatia pumila can produce both sexual flowers and asexual bulbils. However, R. vivipara seldom set seeds, whereas R. pumila have regular seed set. Our aim was to understand the asexual mode of bulbil development and the reasons for sexual failure in R. vivipara. Asexual bulbil development was observed by scanning electron and light microscopy. Pollen viability and germination rate were counted for at least 200 pollen grains in triplicate for each inflorescence. Chromosome counting was performed to confirm R. vivipara as triploid species. The bulbiliferous shoots of both R. vivipara and R. pumila initiate from the upper portions of tubers. As they elongate upward, bulbil clusters generates in each node of the shoot. Bulbils develop several hooked scales on top simultaneously, which facilitate dispersal because they can easily attach to the animal’s fur. Although R. vivipara produces showy flowers in spring, their pollen grains were inviable and unable to germinate in vitro in sucrose solution, when compared with R. pumila. These two bulbiliferous species have diversified their reproductive strategies, with respect to R. vivipara being able to reproduce completely asexually and R. pumila being able to reproduce both sexually and asexually.