Tuesday, October 1, 2013

Portulaca dubia, the "lost" or "dubious" species of Johan Gottlieb and John William Tepper

I am often intrigued by historical plant "types" that have languished in herbarium collections for over a century or more because of their insufficiency or ambiguity and, as such, are no longer generally recognized today. In some cases the pressed material was scanty or poorly pressed, but still considered interesting or unique enough to retain for future reference. The process of naming a new species based on "one-off", incomplete and even infertile specimens is unheard of today. But up until about the 1950s/60s many such specimens were named and dutifully described.

Portulaca dubia Teller ex Poelln. (MEL 58509) is one such "species", the epithet of which in Latin is nominative singular feminine and means "doubtful", "dubious", "undetermined", "difficult", "critical", "precarious", "uncertain" or "subject to change". The epithet "dubia" turns up mainly in older botanical treatises to highlight the fact that the plant specimen on which the name is based was insufficient or could not be separated from other species with any degree of certainty at the time.

The case for Portulaca dubia would have been a  Prima facie / Causa termina for me if not for the addition of the remarkable words by Ferdinand von Mueller on the description: "Different from all known species"! These words induce two nagging questions in me: "Why did von Mueller consider it to be different?" and "Why was he so certain that it was different?"

The description for Portulaca dubia Tepper appears in Karl von Poellnitz treatment of the Portulaca genus "Versuch einer Monographie der Gattung Portulaca L" (p. 295), in Feddes Repertorium Specierum Novarum Regni Vegetabilis 37 1934: 240-320.

58. Portulaca dubia J. G. O. Tepper in Transact. a. Proc. Roy. Soc. S. Austr. XVII (1893) 16.
Perhaps annual, herbaceous, spreading, 7 1/2 - 10 cm high, many branched. Leaves alternate or opposite, narrowly ovate, or oblong, usually obovate, 6-18 mm long, mature leaves soon deciduous, juvenile leaves crowded together into the tips of branches. Axillary hairs numerous, short, persistent. Flowers terminal, sessile, solitary, encircled by 4 or more false involucral leaves. Involucral leaves around 6 mm long, broadly ovate. Tepals 12 mm long or longer, wide, not persisting (?), Pink? Style, stigmatic lobes, the capsule, seeds?
Western Australia: Roebuck Bay, Jan. 1890, J. W. O. Tepper. — "Different from all known species" (F. Mueller). — Insufficiently described!
The original description by Tepper appears in the account "The Flora of Roebuck Bay, West Australia." by J. G. O. Tepper. F.L.S. (Transact. a. Proc. Roy. Soc. S. Austr. XVII, 1893, 17: 16-20). A copy is available online (link following).

In the foreword to the book the author writes that the specimens were "collected by my son (J. W. O. Tepper) during the exceptionally dry years 1889 to the close of 1891. They were submitted to Baron Sir Ferd. von Mueller, F.R.S., for identification; many of them were kindly determined by him; of the rest the genera only were indicated." This entry suggests that the specimen may have been drought-affected at the time of collection.

Below: The location of Roebuck Bay on Google Earth.

View Larger Map

The description of Portulaca dubia Tepper from the book follows here.
— sp. January, 1890. "Different from all known forms."— F. r. M.  
 A low spreading herb, probably annual, 3 to 4 inches, branches  numerous, opposite or alternate, basal leaves soon lost, stipular hairs numerous, very short, more persistent than the leaves;  leaves opposite or alternate, narrow oval, oblong or almost obovate, 1/4 to 3/4 inch, in the specimens nearly all crowded at and near the apex of the branchlets.  Flowers terminal, solitary, sessile between four or more floral leaves. Sepal broadly ovate,  about 1/4 inch. Petals pink (?), 1/2 inch or more, broad, fugacious.  Capsule and seed not seen. The provisional name, P. dubia, is suggested.
By the description alone, this provisional species would seem closest to Portulaca pilosa L. or perhaps even Portulaca amilis Speg. The early collection date and location suggest it may be a native species. However the material recognized today as P. pilosa is considered naturalized, as it is consistently similar throughout its range of distribution in Australia. The lack of variation suggests that it may have spread rapidly from a single introduction or from several introductions which had the same geographical origin. The assumption is that if the taxon had been here all along, we should expect to see significant variation across the range of habitat types and climate zone of its distribution.

However this lack of variation could also indicate that it was a pre-existing species, perhaps rare or restricted originally, and its rapid spread was only initiated when Europeans introduced widespread environmental disturbances. It may have rapidly colonized roadsides and cleared areas, following in the wake of the new settlers. The steady movement of humans and horse drawn vehicles across the landscape would have helped to spread it far and wide in a relatively short space of time.

The "pilosa complex" is characterized by the presence of rather narrow leaves, numerous stipular hairs at the leaf axils, and pink/purple flowers. The Australian material appears intermediate in its characters to the species P. pilosa L. and P. amilis Speg. of the Americas. Admittedly these species are closely related and are in fact treated as synonymous by some authors. They are also quite variable there, and some authors have split off different varieties and species, including P. mundula I. M. Johnst. But it is also worth considering that in Africa there are similar species to P. pilosa L. that are endemic there, such as P. kermesina N.E.Br.. This raises the possibility that Australia might also have at least one representative species of its own in this vast pan-tropical complex.

The specimen at MEL is out on loan, however the curators of the New South Wales Herbarium kindly supplied me with a scan of the specimen sheet. The sheet contains two entire plants (one lacking roots) that are well pressed and surprisingly well preserved for their age. The sheet also includes a number of fragments.

Type specimen of Portuaca dubia Tepper ex Poelln. (MEL 58509).
Reproduced with permission from the National Herbarium of Victoria (MEL),
 Royal Botanic Gardens Melbourne.

I was surprised by the specimens, firstly because they are clearly not Portulaca pilosa, and secondly because they appear different to most other Australian Portulaca that I have seen. The specimens do not appear to be allied to P. filifolia, P. decipiens, P. napiformis, or P. australis. The broadly ovate sepals, broad petals, broader leaves, and shorter stems all rule out P. filifolia. The persistent and numerous stipular hairs surely rule out P. oleraceaP. australis, P. intraterranea, and P. napiformis. It is a pity that the pink colour of the petals had not been noted with absolute certainty, as none of the other species mentioned have pink flowers. The author Urs Eglli places P. dubia tentatively as a synonym of P. pilosa subsp. pilosa, and cites Matthews et. al. (1992). This is clearly incorrect. The only characters that the specimens have in common with P. pilosa are the fibrous root system and the prominent stipular hairs in the axils.

In terms of leaf characters and growth habit, Portulaca dubia is most like P. oleracea or P. intraterranea but is atypical in a number of ways. There are no capsules on the specimens, however there are a number of prominent terminal buds present. The buds are larger than those on P. oleracea and a different shape. They are not laterally compressed but more rounded and the apex is not carinated to form a keel; instead the buds appear to be remarkably conical, and are acute or acuminate in outline. Some even appear to possess a slightly curved apical mucro, but this may have resulted from their positioning during the original pressing process.

The variations in leaf size and shape, from narrowly oblong to obovate and around 2-3 mm to 6-18 mm long is intriguing, as some branches have only leaves that are consistently small, while other branches have leaves that are, for the most part, consistently large. There is multiple branching from each internode and this character alone distinguishes it from the P. oleracea / intraterranea clade. This manner of branching is most commonly seen in Portulaca digyna, and it is to this species that P. dubia may be allied. The specimens present as an abnormally large form of P. digyna. However it is difficult to understand if the specimens may simply be this way due to environmental factors, such as the prevailing drought conditions at the time, grazing livestock, a saline habitat, or disease. In the absence of additional collections the influences of such environmental factors cannot be ruled out.

Except for the multiple branching at the internodes, the species P. dubia may also be similar to the "Portulaca sp. affin intraterranea (or sp. affin. australis?)" that I wrote about in a previous blog entry. Click here to open.

The specimens on the sheet appear to have some flowers, including one which looks fully intact, yet Tepper questions the pink colour of the petals in his description. This implies that he may have written the description at a later time, and the pink colour was based on the recollections of his son who had collected and pressed the specimens. The petals may have indeed been pink, but it is also possible that the flowers were actually yellow or pale yellow but with bright pink or reddish petal bases or stamens. We should consider too that yellow flowers sometimes appear pinkish after pressing and drying.

Portulaca sp. affin intraterranea (or sp. affin. australis?).
This interesting species was photographed on Cape York.
When not in flower it resembles P. australis, except for the more
spreading branches. Photo courtesy of Jill Newland and Roger Fryer.

A biography of Johann Gottlieb Otto Tepper appears on the following page, if you scroll about half way down. [Source: BCSA Inc.]

No comments: