Belongs within: Araliaceae.
Hydrocotyle, the water pennyworts, is a genus of aquatic and semi-aquatic creeping plants. Some species are cultivated in aquaria but they are also known in some areas as invasive weeds. Leaves may be simple or more or less divided into lobes or leaflets (Allan 1961).
Characters (from She, Watson & Cannon): Herbs, perennial. Stem slender, creeping or decumbent, rooting at the nodes. Leaves petiolate; petioles not sheathing; stipules present, entire or parted to base, membranous; blade cordate, orbicular, or reniform. Inflorescence a simple umbel; umbels sometimes densely capitate; peduncles axillary, obsolete to much longer than leaves; bracts present or absent; pedicels very short or extended (best seen in fruiting material). Flowers bisexual. Calyx teeth minute or obsolete. Petals white, greenish or yellow, valvate, ovate, spreading. Stylopodium conic to depressed. Fruit globose or ellipsoid, strongly flattened laterally, base cordate, dorsal surface rounded, glabrous (rarely with white hairs); dorsal and lateral ribs usually conspicuous, slender, acute (rarely obsolete); vittae inconspicuous. Seed face plane to concave; endocarp woody. Carpophore usually absent.
<==Hydrocotyle Linnaeus 1753A61
|--H. alataGK00
|--H. americana Linnaeus 1753 [incl. H. nitens Colenso 1891]A61
| |--H. a. var. americanaA61
| `--H. a. var. heteromeria (Rich.) Kirk 1899 [=H. heteromeria Rich. 1820]A61
|--H. bipinnataJ23
|--H. bonariensis Lam. 1789L95
|--H. callicarpaGK00
|--H. dianthaGK00
|--H. dissecta Hooker 1853A61
|--H. elongata Cunn. 1839 [incl. H. concinna Colenso 1885, H. echinella Colenso 1888]A61
|--H. grammatocarpaLK14
|--H. hirsuta Sw. 1788L95
|--H. hydrophila Petrie 1897 [=H. tripartita var. hydrophila (Petrie) Cheeseman 1906]WJ82
|--H. microphylla Cunn. 1839A61
|--H. moschata Forster 1786A61 (see below for synonymy)
|--H. muscosa Br. ex Rich. 1820WJ82, A61
|--H. natansC55
|--H. novaezelandiae DC. 1830 (see below for synonymy)A61
| |--H. n. var. novaezelandiaeA61
| |--H. n. var. involucrata (Col.) Allan 1961 [=H. involucrata Col. 1887]A61
| |--H. n. var. lobulata Kirk 1899A61
| |--H. n. var. montana Kirk 1899A61
| `--H. n. var. robusta (Kirk) Cheesem. 1906 [=H. robusta Kirk 1899]A61
|--H. piliferaGK00
| |--H. p. var. piliferaGK00
| `--H. p. var. glabrataGK00
|--H. pterocarpa Muell. 1855A61
|--H. pusilla Rich. 1820L95
|--H. ranunculoidesV09
|--H. rotundifoliaDK-DW00
|--H. rugulosaG04
|--H. sibthorpioides Lam. 1789A61
|--H. sulcata Webb & Johnson 1982WJ82
|--H. tripartita Br. ex Rich. 1820WJ82
|--H. umbellata L. 1753L95
|--H. verticillata Thunb. 1798L95 [incl. H. verticillata var. triradiataH93]
`--H. vulgarisK03
Nomen nudum: Hydrocotyle tripartita var. subpilosa Petrie in Allan 1961WJ82
Hydrocotyle moschata Forster 1786A61 [incl. H. colorata Colenso 1886A61, H. compacta Rich. 1820C06, H. sibthorpioides var. laciniata Kirk 1899A61, H. moschata var. parvisolia Carse 1928A61]
Hydrocotyle novaezelandiae DC. 1830 [incl. H. alsophila Col. 1886, H. amoena Col. 1889, H. dichondraefolia Cunn. 1839, H. intermixta Col. 1885]A61
*Type species of generic name indicated
References
[A61] Allan, H. H. 1961. Flora of New Zealand vol. 1. Indigenous Tracheophyta: Psilopsida, Lycopsida, Filicopsida, Gymnospermae, Dicotyledones. R. E. Owen, Government Printer: Wellington (New Zealand).
[C55] Candolle, A. de. 1855. Géographie Botanique Raisonée: Ou exposition des faits principaux et des lois concernant la distribution géographique des plantes de l’époque actuelle vol. 2. Librairie de Victor Masson: Paris.
[C06] Cheeseman, T. F. 1906. Manual of the New Zealand Flora. John Mackay, Government Printer: Wellington.
[DK-DW00] Downie, S. R., D. S. Katz-Downie & M. F. Watson. 2000. A phylogeny of the flowering plant family Apiaceae based on chloroplast DNA rpl16 and rpoC1 intron sequences: towards a suprageneric classification of subfamily Apioideae. American Journal of Botany 87 (2): 273–292.
[G04] Gibson, N. 2004. Flora and vegetation of the Eastern Goldfields Ranges: part 7. Middle and South Ironcap, Digger Rock and Hatter Hill. Journal of the Royal Society of Western Australia 87 (2): 49–62.
[GK00] Gibson, N., & G. J. Keighery. 2000. Flora and vegetation of the Byenup-Muir reserve system, south-west Western Australia. CALMScience 3 (3): 323–402.
[H93] Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).
[J23] James, E. 1823. Account of an Expedition from Pittsburgh to the Rocky Mountains, performed in the years 1819 and ’20, by order of the Hon. J. C. Calhoun, sec’y of war: under the command of Major Stephen H. Long. From the notes of Major Long, Mr. T. Say, and other gentlemen of the exploring party vol. 1. H. C. Carey & I. Lea: Philadelphia.
[K03] Kårehed, J. 2003. The family Pennantiaceae and its relationships to Apiales. Botanical Journal of the Linnean Society 141: 1–24.
[L95] Liogier, H. A. 1995. Descriptive Flora of Puerto Rico and Adjacent Islands: Spermatophyta-Dicotyledoneae vol. 4. Melastomataceae to Lentibulariaceae. Editorial de la Universidad de Puerto Rico.
[LK14] Lyons, M. N., G. J. Keighery, L. A. Gibson & T. Handasyde. 2014. Flora and vegetation communities of selected islands off the Kimberley coast of Western Australia. Records of the Western Australian Museum Supplement 81: 205–244.
[V09] Verdcourt, B. (ed.) 2009. Additions to the wild fauna and flora of the Royal Botanic Gardens, Kew. XXVI. Miscellaneous records. Kew Bulletin 64 (1): 183–194.
[WJ82] Webb, C. J., & P. N. Johnson. 1982. Hydrocotyle (Umbelliferae) in New Zealand: the 3-foliolate species. New Zealand Journal of Botany 120: 163–168.