The Distribution of Species by Indigenous People?

I have often noticed that edible species of Portulacaceae are common around ancient indigenous sites. The tubers (and leaves/flowers) of these species are edible and reputedly quite tasty. Most of the species are so small that they would hardly qualify as a meal on their own. However, we need to consider that drought and widespread bushfires can make for "slim pickings" in the Australian bush. During such times any edible vegetable would have come on to the menu. Species of Portulacaceae are more resilient to drought than non-succulent herbs and grasses, and they frequently occur on bare, rocky, elevated areas that are less prone to the ravages of fire.

The activities of humans may have helped to distribute many species of plants. There is some speculation that Tetragonia tetragonioides ("Warrigal Greens" or "New Zealand Spinach") may be more common today around ancient indigenous campsites and along the old bush trails. There is little doubt that Aboriginal people collected all manner of bush foods which they brought together at the campsites. Seed would have invariably fallen off and become more concentrated in those areas. It is also possible that plants that were used in traditional medicines and ceremonies may show a greater concentration around campsites and ceremonial grounds.

Locally I know of several ceremonial "bora" grounds where the tuberous species Grahamia australiana, Portulaca bicolor and P. australis are very common. Further west I have found those same species, as well as the tuberous Calandrinia pleiopetala sens. lat. in similar high concentrations around the old campsites. In the central west of southern Queensland I have found Grahamia australiana to be locally abundant around ancient Aboriginal rock wells and hearths.

The occurrences may be purely coincidental, given that bare, elevated areas with stony, skeletal or sandy soils are also typically the preferred habitat of Portulacaceae species. However the concentration of species around ancient indigenous sites does suggest to me that indigenous activities may have been a major contributing factor in the distribution of some species. Over many thousands of years, human activities may even account for the widespread distribution of some species today. Grahamia australiana (syn. Anacampseros australiana) for instance, has an extremely large range of distribution, from Cape York in Queensland to the Flinders Ranges in South Australia. It is highly likely that many of the ancient extensions in its distribution can be attributed to human trade and the periodic migration of peoples about the landscape. Food for thought!

Portulaca cyclophylla

All Photos on this page courtesy of Attila Kapitany.

Portulaca cyclophylla Muell. (1890) is a very interesting species with spectacular flowers for its diminutive stature. In habitat, the thick, somewhat leathery leaves are opposite, almost circular, 6-10 mm in diameter, and grey or brown-coloured. Specimens often have a convex upper leaf surface, which is covered by a network of uneven reticulations (i.e. creases and fissures). The result is that the plants blend in perfectly with the gravelly soil surface in which they grow.

The underside of the leaves is usually convex, dark purple, finely reticulated with a leathery texture, and almost translucent.

Although stone mimicry is found most commonly in African succulent species, such as Lithops, it is quite rare in the Australian flora. It occurs in only a handful of species, most being in Portulacaceae.

"Can you see me?"
P. cyclophylla camouflaged against the stony surrounds.

Portulaca cyclophylla has seasonal branches that die back in dry conditions to a swollen perennial taproot. The plant re-shoots after good rains.

The species is similar in many respects to P. bicolor, but differs from that species by the significantly larger flowers and greater stamen count. The flowers of P. cyclophylla are up to 35 mm diameter, are 6-8 petalled and bright yellow, and on a pedicel about 1-1.5 cm long. The stamens are numerous and about half the length of the petals. The greatly exserted stigma has 6(-8) feathery lobes that are much higher than the stamens.

P. cyclophylla frequently shares its habitat with a more robust succulent, Calandrinia schistorhiza Morrison. Both species are largely absent from the Kimberley region, however there are a few sporadic records of P. cyclophylla from the Northern Kimberley region. The two species occur on arid gravel and sand plains in central Western Australia between Newman and Wiluna. They are most commonly found in the Gascoyne, Little Sandy Desert, Murchison, and Pilbara regions of the Eremaean Province.

Thank you once again to Attila Kapitany for his excellent photos!

All Photos on this page courtesy of Attila Kapitany.

Portulaca oligosperma

Portulaca oligosperma F. Muell. (1859) is another of the tropical annuals with opposite leaves and pink-purple flowers. It is prostrate and forms mats to about 100 cm wide. It flowers from February to May.

It grows in woodlands on sandy or loamy soils from the Kimberley region in WA to Normanton in Queensland, with several sporadic records in eastern tropical Queensland (west of the Mulligan Highway).

P. oligosperma is similar in some respects to P. digyna. It differs from that species by:

• 6-petalled flowers, cf. 4(-5) petalled for P. digyna.
• 6 stamens and a 3-lobed stigma, cf. 4(-10) stamens and a 2-lobed stigma for P. digyna.
• common style about as long as the stigmatic arms, cf. common style longer than stigmatic arms for P. digyna. 
• capsule operculum conical and glabrous, cf. turbinate and papillose for P. digyna.
• seeds grey, tuberculate, cf. black and smooth for P. digyna.

Another difference is that the branch segments of P. oligosperma have a slightly divaricating, flexuous habit. This means that the segments of each branch diverge from each other on a slight angle from the nodes, giving the branches a characteristic "zig-zag" habit.

The only photograph that I can find of this species is on the Atlas of Living Australia website.

Portulaca clavigera

Portulaca clavigera R. Geesink was first described in 1969. I have never seen it and know very little about it. I believe it is similar in most respects to Portulaca digyna, but the leaves are broadly obclavate rather than shortly terete, the flowers are sessile instead of pedunculate, and the petals are more rounded.

The following description of Portulaca clavigera R. Geesink is by J.G. West and was published in Flora of the Kimberley Region by J. R. Wheeler, Western Australian Herbarium, 1992, page 136.

Prostrate ephemeral herb, with red stems to 100 mm long. Axillary hairs continuous around the node, to 6 mm long, very prominent giving the stem a jointed appearance. Leaves opposite, subsessile, ovate to elliptic, 5-8 X 3-5 mm, margin revolute in upper half, acute to acuminate. Inflorescence a head of 2-5 sessile flowers. Sepals ovate, 3-4.5 mm long, with a dorsal awn attached just below the apex. Petals 4, bright pink to red, broadly obovate, 5-8 mm long, emerginate. Stamens 12-15. Stigmas 2 on a common style much longer than the stigmatic arms. Capsule ovoid, 3-3.5 mm long; operculum ovoid, with an apiculate apex, at least twice as long as the base. Seeds smooth, shiny, black, globular, 0.8-1 mm long.
Flowers and fruits February -June.

P. clavigera is found only in the northern Kimberley in the far NW of Western Australia, between the Mitchell Plateau and the Prince Regent River. Florabase describes the habitat type as lateritic gravel, sand on sandstone, and basalt outcrops.

The only photo I can find online is this one on WA Florabase.

If anybody reading this post has more information or photos of this species that can be used on this blog, please contact me or leave a message below.

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

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 Herbarium, which 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.

The Question of Environmentally-Induced Variation

In previous posts I may have given the impression that Portulaca are morphologically-unstable, chameleon-like plants, whose frequent mutations allow them to occupy a huge range of habitat types. This was never my intention.

Salinity clearly does influence the morphology of some species or subspecies. But salinity-adapted (or salinity-modified) populations are generally made up of individuals that have consistent and stable characters in that situation. If a population of a different variety or subspecies is encountered at the same location, it too is generally made up of individuals with consistent characters. I have raised the possibility of "intergrades" or "intermediates" in some situations, but I have never been able to prove their existence with any certainty. If they do occur they are probably rare and may well turn out to be distinct taxa in their own right!

I should also state that it is rare to find more than one variant of a Portulaca species at any given location.

Whenever variants of P. oleracea have been grown side by side in cultivation, they have for the most part retained the characters that made them distinct in habitat. Surprisingly, even plants that came from very saline habitats (and their offspring) have often retained enough of their characters in cultivation to suggest that their characters are genetically fixed and unique. If the differences that define a taxa are consistent and can be duplicated, this raises the possibility that these populations may be undescribed varieties, subspecies, or even species.

A variant may still be in the process of evolving, in which case it may be difficult to separate from an already described taxon. This "incomplete evolution" may also provide a reason why many halophytes do not die when they are grown in non-saline soil and provided with rainwater. Some highly specialized halophytes may, on the other hand, become etiolated and pine away if transplanted into a non-saline environment. Others may be less specialized, so will be capable of making the sudden transition to non-saline conditions. These plants may show only limited changes to their physical attributes after changes occur in their environment. The physical modifications that allowed them to cope with salinity may even be retained for many generations in their offspring. In some desert areas, this kind of adaption may give the variant a distinct advantage over any others, as it will be able to survive the transition between the less saline wet season and the more saline dry season. On the other hand, plants that are salinity specialists run the risk of dying out completely during a prolonged wet season, unless they have other strategies in place, such as seed dormancy.

Environmental factors like climate, salinity, and soils (in the long term), along with light, moisture, temperature, and nutrient levels (in the short term), definitely influence the size and vigour of many plant parts. In Portulaca, an increase in one or more of the short-term environmental factors can induce the formation of larger leaves and stems, as well as longer and more numerous branches and roots. However my observations of cultivated specimens suggest that although such changes do occur, the changes are consistent and occur within a range of what can be expected for each of the variants. Furthermore, flower size in Australian Portulaca does not appear to be greatly influenced by short or long term environmental factors. A long period of heat, moisture and sunlight, may increase flower size in some species, such as P. australis and P. intraterranea, but this is something that requires further study.

In the wild, most Australian species will only flower in bright, warm, well-drained situations, and most species occur on nutrient-deprived, gravelly soils. The exception of course is P. oleracea, but apart from an increase in leaf size and branch length, the addition of extra light, moisture and nutrients does not appear to influence the size of the flowers in that species to any significant degree  Likewise, an increase or decrease in any of these environmental factors does not appear to influence the length and number of stamens in any of the species I have studied.  I doubt too that the seed texture will change simply due to a sudden change in the environment. Seed size may of course be reduced by drought, disease or predation, or if the temperature suddenly falls below 10 degrees Celsius for a prolonged period of time. In these cases the seed has most likely been aborted. (Disease symptoms cannot be used as a tool to differentiate taxa!)

I have however noted a significant change in flower size and leaf shape due to changes in the environment in some exotic species, in particular those from the Americas. For instance, P. cryptopetala will often produce tiny flowers about 5 mm diameter with few stamens early in the season, or if plants are positioned in cool conditions or in heavy shade. The flower size increases to about 30 mm diameter as the plants mature in full sunlight. The stamens also become more numerous. Furthermore, the leaves on juvenile plants are often ovate-oblanceolate, but become linear-lanceolate and channeled with somewhat acute tips as the plant matures.

In cool, shaded situations, the exotic species P. pilosa and P. grandiflora can have smaller flowers and develop long, sparse and spindly branches and leaves. But I have not seen any shade-induced variation in these species that was unexpected. The plants can still be easily identified as "shade forms" of their respective species. The same can be said for our native P. filifolia, which is sometimes found in the partial shade of trees and bushes.

Most Australian species will simply fail to grow or flower if positioned in heavy shade. So it may be difficult to determine the influence of shade on the morphology of many native species, except perhaps to say that heavy shade kills them!

In plant populations there is always, as a general rule, more variation evident in the size and shape of the vegetative parts than the flowering parts. The Linnaean System is largely based on this premise. A botanist friend tells me that "Molecular biologists call the gene sequences involved in reproduction "highly conserved"." If anyone is interested, the concepts of "conserved sequences" and "conserved genes" are outlined here.

The apparent "widespread morphological variation" in some of our native Portulaca species is likely masking the existence of a number of distinct taxa. It would be a shame if any potential taxa are not being recognized. A lack of clearly defined, clearly delineated variation in a species or genus can potentially lower the biodiversity in many ecosystems. In the case of rare taxa that remain unrecognized and undescribed, the risk of undocumented extinction events is ever present.