[[alternative]]A Taxonomic Study of Hydrocotyle (Apiaceae) of Taiwan

[[abstract]]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.