Saturday, December 29, 2012

Portulaca filifolia

P. filifolia typically has an erect-diffuse habit, terminal
flowers on long, thin branches, and sparse, terete leaves.
Photo courtesy of Attila Kapitany.

Portulaca filifolia Muell. may at first glance appear similar to P. australis Endl., but the similarities are superficial. In any case they seldom occur together in the wild. The two plants in the following photograph were grown in cultivation for comparison purposes. The prostrate species at left is P. australis, and the more upright and diffuse species at right is P. filifolia. (Click on thumbnails to enlarge all photos.)

P. australis at left and P. filifolia at right.
Photo courtesy of Attila Kapitany.

P. filifolia is widespread in inland Australia. It generally occurs on flat sandy or stony plains, where it grows in full sun or under the sparse cover provided by trees and bushes. It occurs on sandy floodplains, near inland lagoons, and along ephemeral wash areas. It is often found where a shallow lens of light sand has been deposited over heavier clay. It frequently forms part of the sparse ground flora in cypress pine forests and poplar box woodlands.

The plant is generally regarded as an annual. It has an upright, reclining or diffuse growth habit, with stems to about 20 cm long. The leaves are linear and terete, 10-30 mm long and sparsely situated along the branches.

Above: Bright yellow flowers in terminal clusters on a rather
sparse and untidy plant typifies P. filifolia.
Photo courtesy of Attila Kapitany.

Below: Terminal leaves, flowers, and pyxis of P. filifolia.
Photo by Ian Menkins.

The axillary hairs are conspicuous and generally numerous, especially around the terminus of the branches, and are often more than 5 mm long. The hairs apparently suffer the effects of ablation due to wind and rain and possibly also the activities of birds, rodents and insects. As a result, some mature plants may appear to have few or very short axillary hairs. Flowers are terminal and in 3–10-flowered clusters. The petals are (4–)8-10 mm long and yellow, with 12–30 stamens. The sepals are 4-5 mm long. The stigma is longer than the stamens.

Above: P. filifolia, terete leaves and terminal, clustered flowers.

Below: Close up showing stigmatic lobes longer than the stamens.

Photos by Ian Menkins.

The capsules are 3–5 mm long, and the operculum (i.e. the "upper" dehiscing part of the capsule) is rounded or dome-shaped and about twice as long as the lower capsule. The operculum separates below the middle of the pyxis and often retains the withered remnants of the corolla.

P. filifolia, terminal cluster of capsules with one dehisced operculum.
Photo by Ian Menkins.

The seeds may be grey-black or shiny black and the testa cells are basally stellate and most are tuberculate. The tubercles are nippled and pointed and occur in ornate, concentric rows. In rare cases only the marginal or upper tubercles are pointed.

The shape and texture of the testa is illustrated on Plantnet - (Entry for P. filifolia). The following microscope captures are at 20X and 40X magnification and show the subtle variations in seed collected from a single population of P. filifolia. The seed are fairly consistent in size, shape and colour. The testa is for the most part rather black or grey-black in the fresh state, but soon turns steely-grey and somewhat iridescent upon exposure to air and sunlight. Some seeds are brownish due to a coating of fine dust particles. The bases of the tubercles are generally stellate. The tubercles range in shape from colliculate with rather low, oblong and flat summits to raised and prominently nippled. The tubercles are arranged in an ornate series of concentric rings. The margins of the seeds resemble the tread of a tyre if not for the prominent nipples!

This species may or may not have a rather soft, oblong, perpendicular, whitish or creamy taproot or tuber ca. 4 cm long and ca. 6 mm wide. Some secondary tubers may also occur, subtended by fibrous roots. Occasionally the tuber may have multiple constrictions, giving it the appearance of a string of small sausages.

The existence or absence of tubers is something that has baffled me for many years. Last year when I thinned out my excess P. filifolia plants from the sand bed, I noticed that almost every specimen had a tuber. Probably around 98% of the hundred or so plants that I removed had tubers. The tubers were more prevalent on juvenile plants. However, when I thinned out my plants this year I only found two plants with slightly swollen roots and they were mature plants! All of the other plants had only fibrous roots!
Above: P. filifolia plants in different stages of growth from the
summer of 2012-13. The majority of plants had fibrous roots.

Below: One of only two mature plants that showed
any evidence of taproot enlargement or tuber
formation this year, albeit insignificant.
Photos by Ian Menkins.

I can only conclude that the formation of greatly swollen taproots and tubers is not always a reliable trait in some species of Portulaca. It may be a purely adaptive feature that is triggered by the prevailing weather conditions. For instance, if the weather is dry and hot for many months, a survival gene may be triggered so that plants will develop storage tubers. In good seasons when moisture and nutrients are plentiful, the gene will not be triggered. In this case only fibrous roots will continue to grow. The substrate and drainage may also play a part. The contradiction of tuberous and non-tuberous plants has also been noted when studying P. australis. The same explanation may apply, but this interesting feature clearly demands more study. For instance, could Mycorrhizal fungi be involved?

Footnote: Plants in tropical regions that consistently have longer leaves and petals 10-16 mm long may represent P. decipiens (von Poelln.), although the species is currently placed in synonymy with P. filifolia Muell. I have discussed this taxon in the earlier post Problems in Australian Taxonomy and intend to discuss it further in later posts.

A large clump of the naturalized P. pilosa in foreground,
with the native species P. filifolia growing behind it.
Photo courtesy of Attila Kapitany.

Thursday, December 27, 2012

Portulaca australis

A particularly showy specimen of P. australis.
Photo courtesy of Attila Kapitany.

Portulaca australis Endl. is a very widespread species in Queensland but is only occasionally encountered. It can however be locally common in the right kind of habitat, especially in the summer and autumn months following good rainfall. The species has a preference for granite rock platforms in Eucalypt forest, where it frequently occupies narrow cracks and crevices that have accumulated some gravel and humus. Here the plants are often found in the company of lichens and mosses.

Sloping granite rock platforms in Eucalypt forest provide a 
suitable habitat for P. australis and other Portulacaceae.
Photo courtesy of Attila Kapitany.

Sometimes P. australis can be found around the edges of exposed boulders, particularly along ephemeral seepage lines on well-drained sites. It has also been found less commonly on flat, inland plains of lower rainfall, where skeletal soils or gravels overlay hard claypans. In this situation the clay probably acts as a pavement-like barrier which greatly enhances drainage. In the tropics it has occasionally been found close to tidal sand flats and on sand dunes. In all situations sun exposure is generally high, although some shade may occur as a result of boulders, trees, shrubs, grasses, and aspect.

The leaves of P. australis are crowded, especially on juvenile specimens. Leaves are often linear but slightly flattened on young plants, but become more oblong-elliptic with age. The leaves on mature plants are only about 4-10 mm long X 1-4.5 mm wide and have a sub-obtuse apex (i.e slightly rounded off, not quite pointed) with a truncate to tapered base.

Juvenile plants of P. australis (left) and P. pilosa (right) frequently
emerge from crevices in rocks. The specimen at left is growing amidst
lichen-encrusted basalt rocks. The specimen at right has turned red due to high
sun exposure. Photo courtesy of Attila Kapitany.

The species P. australis is similar to P. filifolia Muell., a very widespread native species with sparser, more terete leaves and an upright or diffuse growth habit. P. filifolia is generally found on flat sandy plains in inland areas.

P. australis differs from P. filifolia by having shorter, more crowded leaves, (cf. 10-30 mm long for P. filifolia), a generally more prostrate growth habit, shorter petals (5-6 mm compared to 8-10 mm for P. filifolia), a stigma shorter than the stamens (cf. longer than the stamens for P. filifolia), stigmatic lobes numbering 5-6 (cf. 3-5 for P. filifolia), sepals less than 4 mm long (cf. 4-5 mm long for P. filifolia), and its elongated capsules circumcissing at the middle (cf. below middle for P. filifolia). Generally speaking the flower petals are more rounded for P. australis, but this may not always be the case. Plants of P. australis are generally prostrate, but may become slightly upright in times of high humidity and cloud cover. Juvenile plants of P. australis, P. pilosa, and P. filifolia can be very difficult to tell apart, even if grown side by side, as all three species tend to be prostrate at this time.

P. australis is generally prostrate, especially during dry
conditions (above), but plants may become upright in
shade or during humid, cloudy weather (below). 

Photos courtesy of Attila Kapitany.

P. australis is said to have smaller flowers generally than P. filifolia, but some forms can have quite showy flowers up to about 10 mm in diameter. The flower colour can range from lemon yellow to almost orange.  

P. australis flowers typically have the stigmatic lobes resting
within the stamens and generally not rising above them.
Photos courtesy of Attila Kapitany.

A particularly large specimen of P. australis, which almost appears
to be forming the shape of Australia! This is a cultivated specimen.
Plants in habitat seldom attain this size.

 P. australis typically has a tuberous rootstock which enables plants to survive long periods of drought. Although it is generally regarded as an annual or short-lived perennial, many of the plants I have observed in the wild and in cultivation are long-lived. In drought times and during the cold winters, they will die back almost to ground level leaving just a few very wilted leaves. Plants resprout from a small stem at the top of the tuber year after year. One plant in cultivation lived for about 8 years.

Thickened taproots and secondary tubers of P. australis,
 which enable the species to survive periods of drought.
Photo courtesy of Attila Kapitany.

Footnotes: I have encountered specimens that completely lack a tuber, both in their early stages of growth and at maturity. The flowers are typically larger and often have an orange tint on the petals. Some plants have even had a splash of light red in the centre. Although they will key out to P. australis, I am unsure if these plants are still within the range of variation of P. australis or if they represent a distinct but undescribed taxon. It is also possible that they have resulted from chance vegetative propagation of otherwise tuberous plants.

Although it seems convenient to predict that tuberous plants will all be perennials while fibrous-rooted plants will all be annuals, my observations of wild and cultivated plants suggests that this is not always the case. I have noted that some predominately fibrous-rooted plants have re-emerged from the same rootstock each spring/summer while some predominately tuberous plants have not re-emerged the following year. The variable root structure of some native Portulaca species greatly complicates their taxonomy. Further research is needed to determine if root character is fixed in some populations or individuals, or if it is triggered by environment.

There is anecdotal support for the existence of a yellow-flowered form of P. pilosa in America and Australia, but it is important to remember that P. pilosa always has free stamens while P. australis has basally connate stamens (i.e. the bases of the filaments are organically fused together). The difference is clearly illustrated in the following photo.

P. australis (yellow) growing with P. pilosa (purple).
 P. australis has basally fused filaments and
stigmatic lobes positioned below the anthers.
P. pilosa has free filaments and stigmatic lobes
exserted above the anthers. Photo by Attila Kapitany.

Tuesday, December 25, 2012

Problems in Australian Taxonomy

I have never been happy with Robert Geesink's treatment of Portulaca in Blumea 17(2): 299, 1969.

Geesink unfortunately lumped all of the terete-leafed Indo-Australian species in with the North American species Portulaca pilosa L. He also wrongly assumed that P. pilosa was a species of tropical Indo-Pacific origin rather than American. This caused much confusion. It soon became apparent that Geesink's Portulaca pilosa subsp. decipiens (V. Poelln.) could not be easily separated from two apparently endemic species, namely P. filifolia F. Muell. and P. australis Endl. Moreover the degree of variation was simply too vast to be covered by Geesink's Portulaca pilosa subsp. pilosa.

Hellmut Toelken ponders this dilemma when he authored the section on Portulaca in J. Jessop's Flora of Central Australia (1981) in the late 1970s. On page 40 Toelken writes: "a wider knowledge of Australian populations will show whether P. filifolia, an annual with fibrous roots and a seed coat with all cells nippled, and P. remota a perennial with tuberous roots and a seed coat with cells along the margin nippled, should be included in the wide range of variation of the subsp. pilosa."

An interrogation of the SA Plant Census database shows no entries for P. pilosa or P. remota. In fact all South Australian occurrences of P. pilosa were re-determined in 1981 as P. filifolia F. Muell. The revision unfortunately did not make it into the Flora of Central Australia, which had been published earlier that same year. There were evidently no records of the naturalized American species P. pilosa in South Australia at that time, although it was already common and widespread in New South Wales and Queensland and in the tropical half of Western Australia. However it appears to have unfortunately been confused with at least one yellow-flowered native species in Western Australia, and it is still mistakenly regarded as a native species there. P. pilosa has been recorded from the far north of South Australia in more recent times.

The other species mentioned by Toelken, Portulaca remota Poelln. is now regarded as an unresolved name and is therefore no longer recognized, at least not in Australia. The name may have been applied at a time when botanists did not realize that P. filifolia generally has a small tuber in the early stages of its growth, which it frequently loses upon reaching maturity. At this time the roots become fibrous (from my personal observations of cultivated specimens). However I cannot explain the differences that Toelken noted in the seed coat.

It is difficult to understand how Geesink reconciled the yellow-flowered, mostly upright plants of the native species P. filifolia Muell. with the mostly prostrate, bright pink to purple-flowered plants that we now know to be the tropical American species P. pilosa L. Yet he appeared to be content to suggest that both are mere manifestations of a species that he presumed to be highly variable. One possible reason for this assumption is that Geesink had, at that time, narrowed the focus of his research to the Indo-Pacific region. Considering that P. pilosa already had a widespread presence in this region by 1969, the species must have appeared to Geesink to be representative of a species complex that was endemic to this region.

Geesink's misplaced application of the name P. pilosa in Australia was unfortunate, but he at least understood the wide degree of variation that was evident in Portulaca filifolia Muell. The extremes of this species are illustrated well on page 40 of Flora of Central Australia.

I have long noticed that some plants that key to P. filifolia from the northern tropics frequently have a larger corolla (10-16 mm long), a more upright growth habit and very sparse foliage. These plants are a very good match for the Toelken description of Geesink's Portulaca pilosa subsp. decipiens (V. Poelln.) shown in Fig. 62 above. The seeds of these plants need to be scrutinized carefully against the illustrations and descriptions in Toelken, which show a colliculate seed coat (i.e. one that is covered with lots of small mounds). Toelken describes the seed coat further as having flat oblong elevations that are arranged in dense concentric rings. If any specimens match this description, then these plants may represent a taxon that is indeed distinct from P. filifolia. In this case the Portulaca decipiens of Karl von Poellnitz (1933) should probably be reinstated, given that Geesink gives the distribution of the taxon as "Australia, north of the Tropic of Capricorn".

The type of P. decipiens Poelln. was collected at "Fanny Bay" (presumably Fannie Bay near Darwin) in December 1869 (Coll. No. Fr. Schultz 705). In his description of P. decipiens on page 159 of Repertorium specierum novarum regni vegetabilis XXXIII (1933/1934), von Poellnitz states that the flowers were not seen and this may be the reason why he seems reluctant to place P. filifolia Muell. in synonymy. He writes (German translation):

It is certainly close to P. filifolia F. Muell. and P. sclerocarpa A. Gray*. These two growing in Australia species have also alternate, very narrow leaves and clearly visible axillary hair. P. filifolia has even narrower, threadlike leaves, longer and more numerous axillary hair, and a capsule that opens below the centre. P. sclerocarpa* has also numerous and long axillary hair, a very hard, at the bottom opening capsule, and seeds with a stellate pattern.

Although the "Fanny Bay" specimen was lacking flowers and the description provided by von Poellnitz was rather sketchy, Geesink nevertheless became convinced that P. decipiens Poelln. belonged to a taxon distinct from P. filifolia Muell. He clearly had access to more recent specimens that could be split on the basis of consistent characters.

Hellmut Toelken (1981) clarified the distinction further by separating the two mainly on the basis of flower size, leaf length, and seed texture. But he also suggested that only a greater understanding of Australian populations can resolve the problems that he noted with abberant specimens.

The names of the two taxa could possibly be reworked now as P. filifolia Muell. subsp. filifolia and P. filifolia Muell. subsp. decipiens (Geesink ex Poelln.). This would of course be on the proviso that a sufficient number of consistent specimens be found that are not merely representing extreme forms within the total population. The full range of variation must first be established.

Typical specimens of P. filifolia have an erect to decumbent habit, corolla 4-10 mm long, and seed coat stellate and tuberculate with all or at least the marginal cells prominently nippled (Fig 61). This is true for most of the specimens found throughout inland Australia.

Specimens of P. filifolia differ in all cases from P. australis by the elongated stigma which always places the stigmatic lobes above the stamens.

Bentham and Mueller's key has stood the test of time. Even the somewhat obscure P. napiformis of Mueller is still recognized today. It occurs in far NW Western Australia apparently as a distinct taxon, yet clearly has affinities with P. australis and P. filifolia. I have never seen this species so have no first hand knowledge of it. Mueller described it as a taxon similar to P. australis but with 4 stigmatic lobes, a lack of axillary hairs, an oblong-shaped tuber, very short branches, and black seeds similar to but smaller than P. oleracea. A photo of P. napiformis appears on the Western Australia FloraBase site. I have seen remarkably similar plants here in Queensland, however the resemblance may prove to be superficial.

Footnote: * Portulaca sclerocarpa A. Gray is now known to be native to the islands of Hawaii where it is endemic. The species does not occur in Australia.

Saturday, December 22, 2012

The Search for a "Workable" Key to Australian Portulaca.

I have been searching for a workable key to Australian Portulaca and a comprehensive treatment of the main species. It appears that the best by far is Bentham and Mueller's Flora Australiensis Vol. 1 (1863). The relevant pages can be viewed from these links. (Requires Acrobat Reader).

Flora Australiensis Vol. 1 cover

Flora Australiense Portulaca page 167

Flora Australiense Portulaca page 168

Flora Australiense Portulaca page 169

Flora Australiense Portulaca page 170

The key shown in Stanley & Ross's Flora of SE Queensland Vol. 1 (1983) is one that I often refer to. I personally like this publication's treatment of P. filifolia, P. pilosa and P. australis. In future blog posts I will examine these species in more detail and will also introduce some of the unknown and indeterminate plants that may be found in Queensland.

Thursday, December 20, 2012

The basic taxonomy of a Portulaca plant

Let's start with some very basic taxonomy. Although the initiated among us may find this all a bit tedious, I feel it is probably necessary to get some basic botany out of the way before proceeding any further.

Pictured here is a rather generic Portulaca plant showing its main parts (click on image to enlarge).

The leaves and stems of Portulaca are generally fleshy or succulent with a mostly smooth (i.e. glabrous) surface. Plants are generally prostrate or decumbent, but some species may be upright or ascending. Some species may have prominent hairs in the leaf axils. Flowers range from being small and inconspicuous to large and showy. Flower colour may vary from species to species, but the three most common colours are pink, purple, and yellow. The roots may be tuberous or fibrous and the different species may be perennial or annual.

The seed capsule is technically called a pyxis. Here is some good information about Portulaca fruiting capsules from an Illinois Natural History website.

The pyxis is in two parts and resembles the fruiting body of a Eucalyptus tree (i.e. a "gum nut"). It comprises a lower capsule which holds the seeds and an upper lid (or operculum). The lid separates near the middle of the pyxis and falls off (dehisces) when ripe to spill out the seeds.
Parts of a Portulaca pyxis by Leo Breman (ex flickriver).

Jim Conrad's Naturalist Newsletter also illustrates this well.

Generally the seed is numerous, fine, and granular. Under magnification it is shaped a bit like a snail shell or a flattened spiral. The surface is often rough and covered in tiny stellated (or "star-like") tubercles. Seed of Portulaca oleracea (ex AcornOrganic, Steve Hurst, USDA)