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Hydrocotyle rivularis H.Eichler ex Henwood
Family Araliaceae
Hydrocotyle rivularis H.Eichler ex Henwood APNI*

Description: Plants perennial. Stems prostrate, robust, glabrous, rooting at nodes, roots abundant and fibrous. Stipules 1.6–1.7 mm long, 2–2.2 mm wide, broadly elliptic, entire, white (translucent).

Leaves compound, 3-foliolate, lighter green below, glabrous on both surfaces. Median leaflet orbiculate, (3–)6–11 mm long, (3–)7–13 mm wide, apex comprising 3 lobules, the 2 lateral lobules shorter than the median lobule; median lobule apex obtuse or round, with three teeth of equal length; median leaflet base acuminate. Lateral leaflets 10–11 mm long, 13–15.5 mm wide, incised into two symmetrical or asymmetrical lobes, sinuses c. 30% of lateral leaflet length. Petioles (10–)50–160 mm long, glabrous.

Inflorescence a simple umbel, 7–9-flowered; flowers all hermaphrodite, or with a few apparently male flowers. Peduncles much shorter than subtending petioles, (5–)30–50 mm long, glabrous. Bracts 0.3–0.5 mm long, 0.2 mm wide, ovate, entire, green. Flowers pedicellate; flowering pedicels 1–1.8 mm long. Corolla white (occasionally with margin of petals purple); petals 5, ovate, 0.65–0.75 mm long, 0.4–0.5 mm wide. Filaments white, 0.4 mm long; anthers purple, 0.25 mm long.

Schizocarps ellipsoid, slightly laterally compressed; bases truncate; fruiting pedicels 0.8–2 mm long. Mericarps 0.7–0.8 mm wide, 0.9–1 mm long, dorsal and lateral ribs acute, median ribs not raised; surface between lateral and dorsal ribs convex or flat, smooth, surface between median and lateral ribs convex, smooth. Fruiting styles 0.5 mm long.

Photo J. R. Hosking

Photo J. R. Hosking

Flowering: December to February.

Distribution and occurrence: Endemic to New South Wales and Victoria above c. 600 m altitude.

Found in flowing montane streams, on their margins, or associated with swampland that is regularly inundated. With Montia, various Cyperaceae, Eucalyptus dalrympleana, E. stellulata and E. pauciflora. Petioles and stolons are often submerged, with leaf laminas and umbels floating on the water surface, sometimes forming large masses of foliage.
NSW subdivisions: NT, ST
Other Australian states: Vic.
AVH map***

The specific epithet refers to its preference for growing in (relatively high altitude) streams. Formerly in Apiaceae.

Text by M.J.Henwood
Taxon concept: Henwood,M.J., (2014) Hydrocotyle rivularis: a new trifoliolate species from south-eastern Australia. Telopea 17: 217–222.

APNI* Provides a link to the Australian Plant Name Index (hosted by the Australian National Botanic Gardens) for comprehensive bibliographic data
***The AVH map option provides a detailed interactive Australia wide distribution map drawn from collections held by all major Australian herbaria participating in the Australian Virtual Herbarium project.
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