Homalanthus polyandrus

  • Ligule. Papanui Inlet, Otago Peninsula
  • Caryopsis. Papanui Inlet, Otago Peninsula
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Species

Homalanthus polyandrus

Common Name(s)

Kermadec Poplar

Current Threat Status

2012 - At Risk - Naturally Uncommon

Previous Threat Status

2009 - At Risk - Naturally Uncommon
2004 - Range Restricted

Qualifiers

2012 - IE, RR
2009 - OL

Authority

Homalanthus polyandrus (Hook.f. ex Müll.Arg.) Cheeseman

Qualifiers

OL

Family

Euphorbiaceae

Brief Description

Broad small tree bearing thin wide triangular leaves inhabiting the Kermadec Islands. Twigs bleed white sap. Leaves 5-10cm long, as wide as long, on long stalk to 10cm long. Flowers in a green long spike. Fruit purple with white lines that split to reveal wrinkled yellow seeds.

Flora Category

Vascular - Native

Synonyms

Homalanthus polyandrus (Hook.f.) Cheeseman comb et nom.superf.; Carumbium polyandrum Hook.f ex Müll.Arg.; Carumbium polyandrum Hook.f. nom. inval.

Distribution

Endemic. Kermadec Island group, Raoul and Macauley Islands

Habitat

A successional species of coastal scrub, forest and upland forest, where it usually forms the understorey or is a sporadic emergent. Sometimes, as on old slip scars, it may form the main canopy.

Features

Small, glabrous tree up to 10 m tall. Branches and branchlets slender, rather brittle, terete in cross-section, initially slightly ribbed, leaf-scars prominent. Leaves adaxially dark or bright-green to yellow-green above, sometimes suffused with red (especially new growth), abaxially subglaucous, membranous, stipulate, stipules } 20 mm long, caducous; juvenile lamina up to 300 mm diameter, broadly ovate, truncate or cordate at base, rarely perfoliate, adult lamina 30-200 diameter, usually rather broad-ovate to subrhombic, abruptly narrowed to acute or acuminate apex, cuneate to truncate at base; petioles > or } = to blade. Inflorescences terminal on new growth, racemose. Racemes slender up to 200 mm long, usually with a few solitary long-pedicellate Š flowers below or at base and many solitary short-pedicellate ‰ flowers above (racemes occasionally unisexual); each flower subtended by a caducous, glandular bract and 2 prominent glands at the base of the pedicel Male flowers bearing c.30-35 close-set stamens; perianth segments 1. Female flowers tri-locular with 3 styles, stigma capitate. Fruit } smooth, coriaceous, 3-angled, reddish, 10-12 mm diameter. Seed elliptic, oblong-elliptic or more irregular, terete or somewhat compressed, (2.3-)3.0 - 4.8 mm long, almost entirely covered with a yellowish aril.

Similar Taxa

None in the wild. However has often been confused with the naturalised and very weedy Homalanthus populifolius Graham. From that species is differs by the male flowers which are solitary rather than clusters along the raceme, and female flowers which are tri rather than bi-locular and which have 3 rather than 2 styles.

Flowering

Throughout the year

Main Flower Colour

Black

Other Flower Colour

Black

Fruiting

Throughout the year

Propagation Technique

Easily grown from fresh seed and cuttings, and often naturalises where it has been planted. However, extremely cold sensitive and will not tolerant even a slight frost. Best grown in a warm, sheltered site.

Threats

Formerly seriously threatened with extinction due to feral goats and regarded as extinct on Macauley Island, this species has made a spectacular recovery following the successful goat eradication on Raoul Island (the last goat was shot there in 1986). Homalanthus is now widespread and no longer regarded as threatened. In 2006 it was rediscovered on Macauley Island - though whether this was the original tree seen by Cheeseman or a new arrival is unclear. The species is now listed only because it is still a naturally uncommon, range restricted endemic.

Chromosome No.

2n = 64

Endemic Taxon

Yes

Endemic Genus

No

Endemic Family

No

References and further reading

Gardner, R. 1999. Homalanthus (Euphorbiaceae) in New Zealand and its fruit. Auckland Botanical Society Journal, 54: 6-7

Müller Argoviensis, J. 1864 (3. September): Neue Euphorbiaceen des Herbarium Hooker in Kew, auszugsweise vorläufig mitgeteilt aus dem Manuscript für De Candolles Prodromus. Flora, oder Allgemeine Botanische Zeitung 47(28): 433.

Thorsen, M. J.; Dickinson, K. J. M.; Seddon, P. J. 2009. Seed dispersal systems in the New Zealand flora. Perspectives in Plant Ecology, Evolution and Systematics 11: 285-309

This page last updated on 10 Apr 2015

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