Stachystemon brachyphyllus and S. polyandrus Intermediate

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Stachystemon brachyphyllus and S. polyandrus Intermediate

Stachystemon is a member of the highly diverse Euphorbiaceae family and is distinguished from other genera by the perianth (calyx-like) around individual flowers and the two lobed stigma of female flowers. Both Stachystemon brachyphyllus and S. polyandrus are recorded for the east of Esperance where the above colony was discovered in the second year after a bushfire. However it is not clear if these particular plants are a hybrid between the two, or a transition form as one species evolves to the other, as both appear closely related. I include it here as it is of scientific interest, plus also a pretty little shrub.

Stachystemon brachyphyllus is more of an inland species and recorded from the NE of Esperance at Mt. Heywood and Mt. Ragged (50-60 km or around 35 miles from the south coast) in the mallee region. Stachystemon polyandrus is more of a coastal species basically occurring in non-calcareous heathland. This intermediate form was 30 km from the south coast, growing on a north facing sandy slope (probably over gravel, a heavier soil or even granite) and draining to a substantial clay base flooded area. The colony consisted of over 100 plants in about ½ hectare (100 metres x 50 metres).

Stachystemon polyandrus has already been posted here (see right-hand column) and has yellow to white flowers, with male flowers having between 10-14 stamens. Stachystemon brachyphyllus has a reddish flower with around 25 stamens. There are other small differences, but the colour and stamen number are the most obvious. This intermediate form has the reddish flowers of S. brachyphyllus, but the stamen number of S. polyandrus, plus differs in other respects.

In the 2003 paper of David A Halford and Rodney J.F. Henderson of the Queensland Herbarium, titled A revision of Pseudanthus and Stachystemon, from the Studies in Euphorbiaceae series, they do mention intermediate forms between these species, so presumably other colonies also exist. Plants in this colony were all young and not fully grown, so their ultimate height and development could not be obtained, but at this stage were around 30 cm (12”) in height. They were photographed in mid October, so would likely flower between September and December as do S. brachyphyllus and S. polyandrus, with unseasonable weather extending or shortening this period.

Stachystemon polyandrus – Euphorbiaceae

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Stachystemon polyandrus – Euphorbiaceae

Stachystemon polyandrus is a moderately bushy shrub to 90 cm (3’) in height (mostly shorter), with several clusters of yellow male flowers and one or two individual female ones. The female flower can be identified by the single pair of stigmatic lobes (poking above the male flowers), a feature that places this plant into the Stachystemon genus.

In the 2003 revision of this genus by Halford and Henderson, they give the distribution of this species from ‘near Kulin southwards to Fitzgerald River National Park and to Israelite Bay…’ However the WA Herbarium only lists it to the near north and west of Esperance, which also agrees with my findings, so likely the Herbarium do not have any easterly specimens. But whatever the situation, it is certainly more plentiful to the west of Esperance.

These Stachystemon species appear to have at least a partial dependency on bushfire or soil disturbance, as they are nearly always encountered within a few years of such an event, usually in small reasonably compact colonies. This species favours non-calcareous sand over gravel soils and can be found in roadside gravel pits, although you need to walk around as being small leaved and somewhat nondescript, they tend to blend into other vegetation and go unnoticed.

The small female flowers when fertilised will produce a larger conical seed capsule that can be seen in one of the photographs. Like many Euphorbiaceae they will bloom over a considerable period, particularly if weather conditions are not extreme. Stachystemon polyandrus mostly flowers from September to January, but has been recorded at other times too.

Stachystemon virgatus - Euphorbiaceae

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Stachystemon virgatus - Euphorbiaceae

When I was a young man, a botanist friend said that if I were ever having trouble keying out a plant and could not make sense of the structure, then it would probably belong to the Euphorbiaceae family. Having tested it many times. I fully agree. Stachystemon is one of a number of interesting if not taxing Australian euphorbia genera, with the eye-catching white flowered Wedding Bush Ricinocarpos spp., being among the better known.

To give some idea of the variability of plants within this family; shrubs like the Wedding Bush have large attractive petals, whereas some euphorbias have none at all, some even lack sepals, leaving the sexual organs completely exposed, these too can differ in size from minute to quite large - It has just occurred to me that I may be writing flower porn here, amazing the similarity! Anyway to continue, the stamens per flower can number from one to over twenty. Some female flowers can by the tips of their style lobes, just be seen surrounded by males, whilst female flowers of other Euphorbiaceae, project themselves away from the males on a long stem and look more like a ripening fruit. The euphorbia fruits themselves can vary from a berry, a drupe (peach-like) to a dry capsule. Other major differences exist within this complex family, but the above will I trust provide a glimpse into this botanical labyrinth.

Stachystemon virgatus is a pretty shrub with bright yellow flowers and growing to less than ½ metre (1’6”) in height. It occurs from the Cape Arid region (east of Esperance) to the west of Albany, plus the west coast Busselton district, then again in the Darling Range behind Perth, so is quite widespread. Apparently this species grows in a variety of soils and habitats, but around Esperance I have only seen it in sandy heath, possibly overlying gravel.

Euphorbias rely on the wind and/or insects for pollination and probably for this reason need reasonably open conditions that are naturally created by bushfires, conditions that agree with local sightings of Stachystemon species. Flowering is recorded from September to November, but to find them, you need to be in the right place at the right time, as they are likely to be quickly overgrown by taller vegetation.