Hydrocotyle

Hydrocotyle L.

Hydrocotyle is a genus of ca. 80-100 species, primarily distributed in temperate and more tropical areas. One species, Hydrocotyle vulgaris L., is a more or less widespread native species in Belgium (Lambinon & Verloove 2012).

The genus Hydrocotyle was traditionally placed within the Apiaceae. However, it was rather aberrant and therefore accommodated in a distinct subfamily (Hydrocotyloideae) or even segregated from Apiaceae (Hydrocotylaceae). Recent phylogenetic molecular research (Chandler & Plunkett 2004, Plunkett & Nicolas 2009) has supported exclusion of Hydrocotyle from Apiaceae and places it as a sister clade of Araliaceae. According to Stace (2010) it appears anomalous in both Araliaceae and Apiaceae and it is possibly better treated as a family of its own.

Species of Hydrocotyle often have a bad reputation of undesirable weeds. As such they occur in aquatic or marshy natural environments or in turf.

In addition to the species treated below Hydrocotyle bonariensis Lam., a native of the New World but widely naturalized in warm-temperate regions of the world (including southern Europe; see Medina 2003), was recently recorded as an introduction in a plant nursery (comm. I. Hoste). Like H. vulgaris and H. verticillata it has peltate leaves but its inflorescence is branched and bears several whorls of pedicellate flowers.

1. Leaves peltate === 2

1. Leaves with a deep basal sinus, never peltate === 3

2. Leaves with 9-13 veins. Petiole glabrous. Inflorescence as long as or longer than subtending leaf === Hydrocotyle verticillata

2. Leaves with 7-9 veins. Petiole with long patent hairs, at least in upper part. Inflorescence shorter than subtending leaf (native) === H. vulgaris

3. Plant glabrous. Leaves fleshy, ca. 50-100 mm wide. Fruit distinctly stalked. Aquatic weed === H. ranunculoides

3. Plant pubescent or glabrous. Leaves not fleshy, ca. 10-15 mm wide. Fruit almost sessile. Turf weed === H. novae-zelandiae


Literature:

Carretero J.L. (1997) Hydrocotyle verticillata Thunb. (Umbelliferae) en la flora iberica. Fl. Montiber. 5: 63.

Chandler G.T. & Plunkett G.M. (2004) Evolution in Apiales: nuclear and chloroplast markers together in (almost) perfect harmony. Bot. J. Linn. Soc. 144: 123-147.

Eichler H. (1987) Nomenclatural and bibliographical survey of Hydrocotyle L. (Apiaceae) Part I. Feddes Repert. 98(1-2): 1-51.

Eichler H. (1987) Nomenclatural and bibliographical survey of Hydrocotyle L. (Apiaceae) Part II. Feddes Repert. 98(3-4): 145-196.

Eichler H. (1987) Nomenclatural and bibliographical survey of Hydrocotyle L. (Apiaceae) Part III. Feddes Repert. 98(5-6): 273-351.

Lambinon J. & Verloove F. (avec coll. Delvosalle L., Toussaint B., Geerinck D., Hoste I., Van Rossum F., Cornier B., Schumacker R., Vanderpoorten A. & Vannerom H.) (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.

Medina L. (2003) Hydrocotyle. In: Nieto Feliner G. & al. (eds.), Flora iberica, vol. 10. Real Jardín Botánico, CSIC, Madrid: 24-28.

Plunkett G.M. & Nicolas A.N. (2009) The demise of subfamily Hydrocotyloideae (Apiaceae) and the re-alignment of its genera across the entire order Apiales. Mol. Phylogen. Evol. 53: 134-151.

Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.

Van Valkenburg J. & Pot R. (2008) Landoltia punctata (G. Mey.) D.H. Les & D.J. Crawford (Smal kroos), nieuw voor Nederland. Gorteria 33: 41-49.

Watson M.F. (1997) Hydrocotyle. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 392.