白頭天胡荽

白頭天胡荽學名Hydrocotyle leucocephala Chamisoo & Schlechtendahl、Hydrocotyle leucocephala Cham. & Schltdl.，五加科天胡荽亞科天胡荽屬多年生草本植物，又稱亞馬遜天胡荽、金錢草、香香草，原產於南美洲，株高五至十五公分，植株具匍匐性或挺水性，莖匍匐地面或水中，纖細，有走莖，分枝多，節上背面生不定根，表面會長葉，單葉互生，葉近圓形、腎形、橢圓心狀，五至七淺裂，端部鈍圓，基部V形缺口心形，葉緣五至七淺裂，裂片三淺裂，鈍鋸齒緣，葉長二十至三十公釐，寬十八至二十五公釐，肉質，葉面翠綠、深綠色，放射狀羽狀脈，約七至九條，似掌狀，細脈網狀，托葉膜質，頂端鈍圓或淺裂，長一、二公釐，淡褐色，半透明狀，闊三角形，葉柄長五至十五公分，柄上密被柔毛，兩性花，繖形花序，頂生，著花十八至二十六枚，密生成球形頭花狀，如迷你繡球，分散生於走莖的葉腋處，花序梗長於葉柄，長五至十五公分，被柔毛，花梗短，長一、二公釐，花梗基部有小總苞，膜質，苞片卵形、倒卵形、卵狀披針形，白、乳白、綠白色，花萼合生筒狀，萼齒微小或不明顯，與子房合生，萼片五枚，綠白色，卵狀三角形，花小，花冠幅形、星形，輻射對稱，花徑約一公釐，花乳白、綠白色，花瓣五枚，漸尖形，早落，鑷合狀排列，雄蕊五枚，與花瓣互生，花藥淺褐色，丁字著生，二室，縱裂，雌蕊心皮二枚，合生，花柱二枚，圓柱形，長約不足半公釐，著生於花盤上，幼時內捲，花後向外反曲，基部膨大，成花柱基，圓錐形或扁平，分泌花蜜，子房綠色，扁球形，高與徑不足一公釐，厚不足半公釐，子房下位，子房一、二室，中軸胎座，或說基生胎座，每室具胚珠一枚，扁狀橢圓球形，離果，扁圓形，長一、二公釐，寬約一公釐，基部心形，光滑，熟後常呈黃褐色，中稜與背稜顯著，側邊扁平，雙懸果，分果片二枚，近無果瓣柄，果熟分離，果頂有天線狀花柱，二枚，種子半圓形，扁平狀。

天胡荽(Hydrocotyle)屬原屬於繖形科，依APG II分類法移入五加科。

天胡荽(Hydrocotyle)屬常見之品種有：
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Hydrocotyle acutiloba
Hydrocotyle algida
Hydrocotyle asiatica(雷公根) 註：歸雷公根屬(Centella)
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Hydrocotyle batrachium(台灣天胡荽)
Hydrocotyle benguetensis(菲島天胡荽、呂宋天胡荽)
Hydrocotyle bonariensis(大葉銅錢草)
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Hydrocotyle calcicola(石山天胡荽)
Hydrocotyle callicarpa
Hydrocotyle changanensis(長安天胡荽)
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Hydrocotyle delicata(姬天胡荽)
Hydrocotyle dichondroides(毛天胡荽、毛柄天胡荽)
Hydrocotyle dichondroides var. dichondroides(毛天胡荽)
Hydrocotyle dichondroides var. tatunensis(大屯山天胡荽)
Hydrocotyle dielsiana(裂葉天胡荽)
Hydrocotyle dissecta
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Hydrocotyle foveolata
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Hydrocotyle geraniifolia
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Hydrocotyle heteromeria
Hydrocotyle himalaica(喜馬拉雅天胡荽)
Hydrocotyle hirta
Hydrocotyle hookeri(阿薩姆天胡荽)
Hydrocotyle hookeri subsp. chinensis(中華天胡荽)
Hydrocotyle hookeri subsp. handelii(普渡天胡荽)
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Hydrocotyle javanica(爪哇天胡荽)
Hydrocotyle javanica var. chinensis(中華胡荽、地彈花)
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Hydrocotyle keelungensis(基隆天胡荽)
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Hydrocotyle leucocephala(白頭天胡荽、金錢草、香香草)
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Hydrocotyle moschata
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Hydrocotyle nepalensis(乞食碗、紅馬蹄草)
Hydrocotyle novae-zelandiae
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Hydrocotyle pedicellosa(大雷公根)
Hydrocotyle peduncularis
Hydrocotyle peltiformis
Hydrocotyle podantha(柄花天胡荽)
Hydrocotyle prolifera
Hydrocotyle pseudoconferta(密繖天胡荽、密傘天胡荽)
Hydrocotyle pterocarpa
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Hydrocotyle ramiflora(長梗天胡荽)
Hydrocotyle ranunculifolia(毛茛葉天胡荽)
Hydrocotyle ranunculoides
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Hydrocotyle setulosa(阿里山天胡荽、刺毛天胡荽)
Hydrocotyle salwinica(怒江天胡荽)
Hydrocotyle sibthorpioides(天胡荽、南美天胡荽)
Hydrocotyle sibthorpioides var. batrachium
Hydrocotyle sibthorpioides var. sibthorpioides(原變種)
Hydrocotyle sibthorpioides var. tuberifera(基隆天胡荽)
Hydrocotyle sibthorpioides 'Crystal Confetti'
Hydrocotyle sibthorpioides 'Lawn Pennywort'
Hydrocotyle sibthorpioides 'Variegata'
Hydrocotyle sp. australia(澳洲天湖葵)
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Hydrocotyle trachycarpa
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Hydrocotyle umbellata(繖形天胡荽)
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Hydrocotyle verticillata(銅錢草、錢幣草、銅幣草、圓幣草、南美天胡荽)
Hydrocotyle vulgaris(野天胡荽、香菇草、盾葉天胡荽)
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Hydrocotyle wilfordii(腎葉天胡荽、惠氏天胡荽)
Hydrocotyle wilsonii(鄂西天胡荽)
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