Wednesday, February 13, 2013

Portulaca digyna

Portulaca digyna, F. Muell. (1859) is a lovely little procumbent annual with opposite, fairly symmetrical branches up to about 10 cm long. The flowers are small, but bright purple and may be numerous on large, mature plants. The species appears after good summer rainfall events, usually in woodlands or on sandy or gravelly floodplains. It quickly forms dense colonies which can sometimes carpet the ground in vibrant purple. It is opportunistic in the way it colonizes bare, scraped ground or roadside drains, but only in those areas that it naturally inhabits.

The leaves are very shortly petiolate, opposite, shortly sub-cylindrical or narrowly oblong, and are up to about 7.6 mm long and a few mm wide. The axillary hairs are very short but conspicuous  The flowers are pink, small, shortly pedicellate, single or in clusters of 2-3. The flowers are surrounded by 2 or 4 involucral-like leaves which form opposite, symmetrical, leafy cymes. The sepals are generally no longer than about 3.8 mm long. The petals number 4 and are longer than the sepals. The stamens number about 10. The style is long and exserted, with 2 long linear stigmatic branches. The style lobes are narrow and tapering to a point. The ovules number about 6, and the funicles form 2 clusters. The capsule is elongate-conical, covered in the upper part with oblong papillae. The seeds number 1, 2, or 3, and are black, smooth, and shining. 

The following description of Portulaca digyna, F. Muell. has been adapted from Flora of the Kimberley Region by J. R. Wheeler, Western Australian Herbarium, 1992, page 137; and the Illustrated Handbook of Succulent Plants: Dicotyledons by Urs Eggli, 2002, page 406. For the most part the descriptions were compatible, but there were some discrepancies; for instance the Eggli publication gives the stamen count as (6-)10(-15), compared to 4 in the description provided in Wheeler!! On the basis of the photos (in the links below), which show stamens numbering 7-8, I have decided to use both. Given the very wide range of distribution, it is possible that two or more distinct taxa are presently being placed in P. digyna.

Prostrate annual herb, with stems to 150 mm long, usually covered in papillae which are most conspicuous on stems and operculum. Axillary hairs inconspicuous, 0.2- 0.8 mm long. Leaves opposite, subsessile or with a petiole 0.5-1 mm long, broadly ovate or circular to narrowly elliptic, 3-5(-8) X 2.5-5 mm, obtuse and apiculate. Inflorescence a many-flowered cyme (-17 flowered, occasionally with 2 central flowers); nodes with 1-2 deltoid, caducous scales; pedicels ca. 1 mm long. Sepals broadly ovate, 1.5-2 mm long. Petals 4 (occasionally 5?), pink to purple, elliptic, 1.8-2 mm long X 2.2 mm wide. Stamens (4-6-)10(-15)  filaments ca. 0.8 mm long; style ca. 0.7 mm long; stigmas 2, on a common style longer than the stigmatic arms. Capsule subovoid, 3-5.5 mm long: operculum turbinate and constricted above the middle, 2.5-3 times as long as the base, papillose in upper half. Seeds black, obovoid to globular, 0.8-0.9 mm long, shiny, smooth.
Flowers and fruits April-June.

P. digyna is found in tropical northern Australia in open woodland. The great botanist Ferdinand von Mueller described it from material collected on the Upper Victoria River, Hooker's Creek, and Start's Creek. Today it is known from about Mt. Isa in Queensland to Wyndham in Western Australia.

The following photos were taken by Russell Cumming, who kindly allowed me to link to them:

Photo 1

Photo 2

Photo 3

Photo 4

Photo 5

Photo 6

Photo 7

Photo 8

Photo 9

No comments: