Saturday, February 9, 2013

Portulaca decipiens

Portulaca decipiens Poelln. (1933) is widely accepted today as a synonym of P. filifolia Muell. (1859). It is still recognized as Portulaca pilosa subsp. decipiens (Poelln.) Geesink by the Australian National Herbariumwhich probably follows Toelken's 1981 cursory treatment of the central Australian Portulaca genus.

Portulaca decipiens had been earlier reduced to a synonym of P. pilosa by Geesink. However, Geesink's revision was based on the erroneous assumption that P. pilosa was native to the Asia-Pacific region. As a result he placed many of the region's terete-leaved species into P. pilosa, irrespective of geographical boundaries and habitat constraints. These placements have been largely rejected today. 

P. decipiens is most closely allied to P. filifolia. It does have several characters that distinguish it from P. filifolia sensu stricto, which may support its treatment as a subspecies of P. filifolia or as a species in its own right.

The illustration in the section on Portulaca in J. Jessop's Flora of Central Australia (1981: 40) shows the two extremes in the P. filifolia "clade". The incidence of "intergrades" and "intermediates" has not been documented but definitely requires further investigation.

The following description is from Toelken (1981).

P. decipiens occurs north of the Tropic of Capricorn and differs from P. filifolia in the following ways: -

•        longer leaves (20-35 mm long, cf. 8-20 mm long for P. filifolia)
•        longer petals (10-16 mm long, cf. 4-7 mm for P. filifolia).
•        longer branches (up to 40 cm long, cf. 10-25 cm long for P. filifolia),
•        wider branches (5-8 mm diameter at their base, cf. 2-4 mm for P. filifolia).

More research is needed to determine if P. decipiens has a consistently colliculate seed coat (i.e. one that is covered with lots of small mounds). Toelken (1981) describes the seed coat further as having flat oblong elevations that are arranged in dense concentric rings. 

Populations that consistently match these descriptions may represent a taxon that is indeed distinct from P. filifolia and worthy of species or subspecies rank.

Generally speaking, the leaves of P. decipiens are more filamentous than P. filifolia,  the axillary hairs are longer and more dense, and the growth habit is more erect. The flowers are slightly more "campanulate" than those of P. filifolia.

The plants in the photos at this link are a good match for the description of P. decipiens, despite the different name proposed in the title. Thank you to Russell Cumming for allowing me to link to his photos. Russell's photostream provides 6 photos of this species. He also has photographs of other Portulaca species from the tropics, some of which may be undescribed taxa.

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