本研究利用外部形態、花粉形態、細胞學及生態與地理分布等資料，針對臺灣產繖形科 (Apiaceae)天胡荽屬 (Hydrocotyle)植物進行分類研究。研究結果顯示在外部形態上，葉片形態、葉表面被毛形態、葉柄被毛形態、花序生長形式、花序總柄長短、花序中小花數目、果實表面微細形態是種間區別的重要特徵。生長形式、葉片微細形態、葉片大小、地理分布亦可作為分類依據的參考。花粉形態方面，花粉表面紋飾在種間具有差異，亦可作為分類依據的佐證。

細胞學研究方面，本研究共檢視了6個類群的染色體數目。其中，H. javanica (2n=ca. 66)與H. ramiflora (2n=ca. 84)兩個類群檢視結果與前人 (Liu et al., 1961)研究結果不同。阿里山天胡荽 (H. ramiflora)之染色體數目 2n=ca. 84為首度報導。

根據研究結果，將臺灣產天胡荽屬處理為8個種2個變種，共10個分類群。發現一個新的變種大屯山天胡荽 (H. dichondroides var. tatunensis)以及訂正兩個被鑑定錯誤的種類姬天胡荽 (H. delicata)及毛茛葉天胡荽 (H. ×ranunculifolia)，並且依據形態中間型和花粉可染率偏低，推測毛茛葉天胡荽為臺灣天胡荽 (H. batrachium)與大屯山天胡荽 (H. dichondroides var. tatunensis)之天然雜交。發現長期被忽略的兩個類群爪哇天胡荽 (H. javanica)和毛天胡荽 (H. dichondroides var. dichondroides)。確認長期沒有採集記錄的基隆天胡荽 (H. keelungensis)之存在，並將其處理為天胡荽的變種階級H. sibthorpioides var. tuberifera。

The genus Hydrocotyle (Apiaceae) in Taiwan was taxonomically revised based on morphological, palynological, cytotaxonomic, phytogeographical, and ecological studies. Morphology of leaves, vesture of leaf-blades and petioles, inflorescence, length of peduncles, flower number in single umbel, and micro-morphology of fruits are important characters for the classification of Taiwan taxa. Stem form, distribution, sizes of leaf-blade, and micro-morphology of leaves also provide useful application. Palynologically, sexine sculpture shows interspecific difference.

Cytologically, chromosome numbers of six Taiwan Hydrocotyle were counted. The counts of H. javanica (2n=ca. 66) and H. ramiflora (2n=ca. 84) from this study are not congruent with previous study (Liu et al., 1961). The chromosome number 2n=ca. 84 is reported for H. ramiflora from Taiwan for the first time.

As a result, eight species and two varieties, including one new variety - H. dichondroides var. tatunensis, were treated. Two erroneous names, H. benguetensis and H. dichondroides were corrected as H. delicate and H. ×ranunculifolia respectively. A natural hydrid Hydrocotyle ×ranunculifolia, putatively derived from H. batrachium and H. dichondroides var. tatunensis, was recognized based on intermediate morphology and extremely low stainability of pollen grains. The rediscovery of H. javaica and H. dichondroides var. dichondroides, which has been ignored for a long time, is also documented. Based on the re-collection of H. keelungensis, a species has never been collected except the type collection, the author treats it as synonymy of H. sibthorpioides var. tuberifera (Ohwi) Yamazaki.

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