Hydrocotyle

Hydrocotyle, also called floating pennywort, water pennywort, Indian pennywort, dollar weed, marsh penny, thick-leaved pennywort and white rot, is a genus of prostrate, perennial aquatic or semi-aquatic plants formerly classified in the family Apiaceae, now in the family Araliaceae.

Description
Water pennyworts, Hydrocotyles, are very common. They have long creeping stems that often form dense mats, often in and near ponds, lakes, rivers, and marshes, and some species in coastal areas by the sea.
 * Leaves: Simple, with small leafy outgrowth at the base, kidney shaped to round. Leaf edges are scalloped. The leaf surfaces of Hydrocotyle are prime grounds for oviposition of many butterfly species, such as Anartia fatima.
 * Flowers: Flower clusters are simple and flat-topped or rounded. Involucral bracts at the base of each flower. Indistinct sepals.
 * Fruits and reproduction: Elliptical to round with thin ridges and no oil tubes (vitta) which is characteristic in the fruit of umbelliferous plants.
 * The prostrate plants reproduce by seed and by sending roots from stem nodes.

Selected species
The genus Hydrocotyle has between 75 and 100 species that grow in tropical and temperate regions worldwide. A few species have entered the world of cultivated ornamental aquatics. A list of selected species:
 * Hydrocotyle americana L. — American marshpennywort
 * Hydrocotyle asiatica L. is now correctly known as Centella asiatica
 * Hydrocotyle batrachium Hance
 * Hydrocotyle benguetensis Elm.
 * Hydrocotyle bonariensis Lam. — largeleaf pennywort
 * Hydrocotyle bowlesioides Mathias & Constance — largeleaf marshpennywort
 * Hydrocotyle calcicola
 * Hydrocotyle dichondroides Makino
 * Hydrocotyle dielsiana
 * Hydrocotyle heteromeria — waxweed
 * Hydrocotyle hexagona
 * Hydrocotyle himalaica
 * Hydrocotyle hirsuta Sw. — yerba de clavo
 * Hydrocotyle hirta
 * Hydrocotyle hitchcockii
 * Hydrocotyle hookeri
 * Hydrocotyle hydrophila - endemic to New Zealand
 * Hydrocotyle javanica Thunb.
 * Hydrocotyle keelungensis Liu, Chao & Chuang
 * Hydrocotyle laxiflora DC.
 * Hydrocotyle leucocephala Cham. & Schltdl. — Brazilian pennywort
 * Hydrocotyle mannii Hook.f.
 * Hydrocotyle microphylla A.Cunn.
 * Hydrocotyle moschata G. Forst. — musky marshpennywort
 * Hydrocotyle nepalensis Hook.
 * Hydrocotyle novae-zelandiae DC.
 * Hydrocotyle phoenix A.J. Perkins — fire pennywort
 * Hydrocotyle prolifera Kellogg — whorled marshpennywort
 * Hydrocotyle pseudoconferta
 * Hydrocotyle pusilla A. Rich. — tropical marshpennywort
 * Hydrocotyle ramiflora
 * Hydrocotyle ranunculoides L. f. — floating marshpennywort, floating marshpennywort, floating pennyroyal
 * Hydrocotyle salwinica
 * Hydrocotyle setulosa Hayata
 * Hydrocotyle sibthorpioides Lam. — lawn marshpennywort
 * Hydrocotyle tambalomaensis
 * Hydrocotyle tripartita
 * Hydrocotyle umbellata L. — manyflower marshpennywort, umbrella pennyroyal
 * Hydrocotyle verticillata Thunb. — whorled marshpennywort, whorled marshpennywort, whorled pennyroyal
 * Hydrocotyle vulgaris L. — marsh pennywort, common pennywort
 * Hydrocotyle wilfordii
 * Hydrocotyle wilsonii
 * Hydrocotyle yanghuangensis

Distribution
Hydrocotyleae grow in wet and damp places in the tropics and the temperate zones.

Fossil record
One fossil fruit of a Hydrocotyle sp. has been extracted from borehole samples of the Middle Miocene fresh water deposits in Nowy Sacz Basin, West Carpathians, Poland.