台灣產台灣水龍（柳葉菜科）的保育

Conservation of Ludwigia _ taiwanensis (Onagraceae) in Taiwan

台灣水龍（2n=24）為二倍體的黃花水龍（n=8）及四倍體白花水龍（n=16）的三倍體天然雜交種，其花色介於二父母種之間，偶具漂浮的氣生根，因染色體分離及配對的困難造成雜交物種的不稔，野外族群或人工雜交產生之後代皆不能結實。台灣水龍雖已知為雜交起源，然其親本之一的黃花水龍並未分布於台灣，推測其起源來自中國大陸東南省份，雜交F1世代的種子藉由候鳥或與稻米種子混合藉由人為引入傳播至本島。本研究除調查其族群目前在台灣的分布外﹐並藉由分子證據顯示其遷徙歷史，根據 RAPD（Random Amplified Polymorphic DNA）實驗針對10個族群利用25個引子進行遺傳多型性偵測，未見任何族群內或族群間的遺傳變異。推測台灣水龍在本島的演化係藉由單一來源之移入後，經由無性繁殖擴大其族群。台灣水龍昔日為習見雜草，近年因受工業及農藥污染水質以及河岸水泥化的影響，其族群正快速退縮中，提升河川水質及棲地的保護為保育本物種最佳策略。 Ludwigia _ taiwanensis (2n = 24) is a member of sect. Oligospermum, consisting of nine species ofwidespread, phenotypically plastic herbs that occur in wet habitats in both the New and Old Worlds. It is a natural,triploid hybrid (2n = 24) between L. peploides ssp. stipulacea, a diploid with n = 8, and L. adscendens, atetraploid with n = 16. Owing to the failure of chromosomal pairing during meiosis, plants of L. _ taiwanensishave pollen and seed sterile. Although L. _ taiwanensis has been known as a natural hybrid in Taiwan, L.peploides ssp. stipulacea, one of its putative parents, does not occur in this island. It was suspected that L. _taiwanensis originated from southern provinces of mainland China. Hybridized seeds may have been carried toTaiwan through migratory birds or by accidental human introduction via agricultural (rice) practices. In this studywe used RAPD (RandomAmplified Polymorphic DNA) fingerprinting to test the single migration hypothesis.Based on banding patterns of ten populations revealed by 25 oligo random primers, no genetic variation wasdetected either within or among the populations. We suggest that the hybridized seeds dispersed to Taiwan viasingle introduction, and spread to aquatic habitats subsequently via asexual proliferation. Plants of L. _taiwanensis used to be a common weed of river banks, ponds and ditches. Their populations, however, havedeclined drastically for the past decade owing to the water pollution from industrial wastes and herbicides as wellas to the cementation of river banks. Habitat preservation is suggested to the best approach for conservation of L._ taiwanensis.