以形態、分子與珠芽發育特徵研究臺灣目賊芋的側系群分類

Abstract

臺灣目賊芋(Remusatia vivipara (Lodd.) Shott)是臺灣列為稀有瀕危的天南星科植物，但其分佈範圍除了在東南亞外，更遠至非洲及澳洲。由於具有珠芽無性生殖構造，因此被歸為是一種兼具有性生殖及無性生殖的珠芽植物，但是在標本館存放的標本尚未見到附帶種子的植株標本。根據前人的形態觀察研究，多依據珠芽特徵將天南星科另外三種歸為目賊芋屬（Remusatia），包括：雲南岩芋(Remusatia yunnanensis)、早花岩芋(Remusatia hookeriana)及曲苞岩芋(Remusatia pumila)。但是早花岩芋及曲苞岩芋在花部形態，卻明顯不同於臺灣目賊芋及雲南岩芋。 本研究第一章除介紹目賊芋屬的生殖方式外，並詳述臺灣目賊芋的分類現況及研究取材的理由。其餘章節依據取自臺灣、中國雲南及泰國不同目賊芋屬的族群個體，探討臺灣目賊芋的側系群分類、珠芽發育、小孢子形成及花芽促進過程。 第二章在探討分子親緣關係，利用核基因：ITS、phyC及葉綠體trnL-trnF、trnH-psbA基因等四段標記進行目賊芋屬歸群。結果顯示目賊芋屬可區分為三群，臺灣目賊芋的葉綠體及核基因序列與雲南岩芋相同歸為一群，而曲苞岩芋及早花岩芋在基因序列分析結果，明顯不同於臺灣目賊芋與雲南岩芋，各自成為一群。 第三章發表生長於臺灣南投縣的新紀錄種植物雲南岩芋，該種原為中國特有種。雲南岩芋與臺灣目賊芋極為相似，兩者只有在佛焰苞檐部顏色的不同，雲南岩芋的佛焰苞檐部為紫紅色，而臺灣目賊芋的佛焰苞檐部為黃色，本文並提供雲南岩芋之特徵描述、圖片與目賊芋屬之檢索表（Published in Taiwania, 58(1): 76-79, 2013）。 第四章探討岩芋 (臺灣目賊芋) 和曲苞岩芋的生殖機制，包含有性花和無性繁殖珠芽的差異。岩芋很少產生種子，而曲苞岩芋卻是常形成種子與珠芽。本研究的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。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（Published in Taiwania, 59(3): 220-230, 2014）。 第五章探討利用生長激素促進臺灣目賊芋開花的可能性，實驗是以0, 25, 50, 75, 100 ppm不同濃度的渤素來處理不同大小的塊莖(平均直徑2.67公分)。結果激渤素處理對直徑1.8 公分以上的塊莖有促成花芽生成的機會，但花序的大小則由塊莖的大小來決定（Published in Taiwania, 60(1): 1-7, 2015）。 第六章綜合前面的研究結果，臺灣目賊芋的生殖策略以無性珠芽為主，曲苞岩芋在親緣關係上則明顯異於其他目賊芋屬的物種。至於小孢子形成的過程及目賊芋屬的親緣關係，未來可以本研究的結果為基礎進一步加以探討釐清。

Remusatia vivipara (Lodd.) Schott is listed as a Vulnerable (VU) species in the Red Lists of Taiwan. Remusatia species are among the few tropical aroids which can have both sexual flowers and asexual bulbils growing in their life cycle. Within Remusatia, R. vivipara is the most widespread in tropical Asia and Africa, while the other species restricted to S and SE Asia except R. yunnanensis which is endemic in Yunnan, China. However, this taxonomic grouping solely based on the existence of bulbil as the genus single diagnostic character has been widely argued, because the morphological characters of inflorescence (especially the spathe) are very different. This dissertation focuses on phylogenetic and taxonomic studies of Remusatia species. There are six chapters in this study: In Chapter 1, the taxonomical status of Remusatia vivipara in Taiwan was introduced. Other chapters dealed with phylogenetic analysis, bulbil development, microsporogenesis and flowering induction of R. vivipara. In Chapter 2, we sequenced two plastid (trnL-trnF and psbA-trnH) and two nuclear (ITS and phyC) DNA regions in resolving the phylogenetic relationships. The genus Remusatia is not monophyletic and could be divided into three subgroups in which R. vivipara and R. yunnanensis formed a clade, R. pumila sistered with Studnera species in another group, while R. hookeriana was sistered to Colocasia species. Based on the phylogenetic trees and morphology of Remusatia species, R. pumila seems to belong to Remusatia and R. yunnanensis is genetically not different from R. vivipara. It is suggested that R. pumila is probably better restored to the genus Gonatanthus. In Chapter 3, we document the discovery of Remusatia yunnanensis (H. Li & A. Hay) A. Hay from Nantou County in central Taiwan. R. yunnanensis has before been considered endemic to Yunnan, China. Remusatia yunnanensis is similar to R. vivipara and only distinguishable by the difference in spathe limb color. The spathe limb of R. yunnanensis is distinctly purple red while that of R. vivipara is yellow. The description and illustration of R. yunnanensis, including a dichotomous key description for Remusatia in Taiwan were provided. In Chapter 4, the reproductive strategies between Remusatia vivipara and R. pumila were compared. Both species can produce sexual flowers and asexual bulbils. However, R. vivipara rarely sets seeds and appears largely on asexual reproduction by bulbils and tubers, whereas R. pumila has regular seed set. This chapter tried to understand the asexual mode of bulbil development and the reasons for sexual failure in R. vivipara. The developments of asexual bulbils from stolons were observed in R. vivipara by using scanning electron microscope and light microscope. Results showed that the bulbils of R. vivipara occurred on independent bulbiliferous shoots rather than on inforescences, and were different from other bulbiliferous plants. Each bulbil was covered with hooked scales which were actually an elongation of bulbil top cells. These hooked scales on bulbils appeared to be unique in Araceae. With the hooked scales, the bulbils might be easily dispersed by birds and mammals in long distance. This might be reflected by the widespread distribution of R. vivipara in Taiwan, SE Asia and Eastern Africa. In addition, chromosome counting was performed to confirm R. vivipara as triploid species. In Chapter 5, the effect of applying Gibberellic acid (GA3) to promote inflorescence initiation and elongation in R. vivipara was evaluated. Tubers of various sizes (average 2.67 cm in diameter) were treated with different concentrations of GA3 (0, 25, 50, 75 and 100 mg L-1). Our results showed the induction of flowering by GA3 at and above 25 mg L-1. However, no significant differences were observed among different GA3 concentrations in terms of inflorescence characteristics and vegetative growth. To produce R. vivipara as an ornamental plant, it is recommended to drench plants with 25 mg L-1 GA3. The present study also revealed that large tuber size made more significant contributions to the prediction of flowering, and the magnitude of inflorescence characteristics (inflorescence length, male zone length, female zone length, spathe length and sterile zone length) and vegetative growth (fresh and dry bulbil stolons) mostly increased with increasing tuber size. The final chapter draws an overall conclusion from the research findings, which could shed light on the reproductive biology of Remusatia vivipara, the unique bulbil developmental pattern and its phylogenetic affinity. Further examinations on pollen meiosis, stamen and ovule developments in R. vivipara are necessary. The application of nuclear DNA markers may also provide a remarkable contribution to the revision of the genus Colocasia and its relationship with R. hookeriana.