Cassia Helmsii

''Senna artemisioides'', commonly known as silver cassia, is a species of flowering plant in the family Fabaceae and is endemic to Australia, where it is found in all mainland states and territories. It is a shrub with pinnate leaves, the leaflets variable, yellow flowers mostly occurring in winter, and linear pods. Six subspecies, four hybrid subspecies and two subspecies named but not yet described are accepted by the Australian Plant Census.

Description

''Senna artemisioides'' is a shrub that typically grows to a height of high and has pinnate leaves, the leaflets in pairs of one to eight, with a sessile gland between the lowest pair of leaflets. The leaves have tiny, triangular stipules, but fall off as the leaves mature. The flowers are yellow and borne in clusters of two to fifteen in leaf axils on a peduncle up to about long, the petals long, each flower on a pedicel up to about long. The sepals are long and greenish, the petals mostly long. There are ten fertile stamens, the anthers long. The fruit is a glabrous, linear pod long, wide.

Taxonomy and naming

This species was first described in 1825 by Augustin Pyramus de Candolle, who gave it the name ''Cassia artemisioides'' in his '' Prodromus Systematis Naturalis Regni Vegetabilis'', from an unpublished description by Charles Gaudichaud-Beaupré of specimens collected by Charles Fraser. In 1989 Barbara Rae Randell raised the genus '' Senna'' in the ''Journal of the Adelaide Botanic Gardens'', and transferred ''C. artemisioides'' to the new genus as ''S. artemisioides''. The Latin specific epithet (''artemisioides'') means "resembling '' Artemisia''", a different group of plants often known as wormwood.

''Senna artemisioides'' is known as wormwood senna in the U.K., and as silver senna in the U.S., where it is an introduced species.

As of May 2023, the names of six subspecies of ''S. artemisioides'' are accepted by the Australian Plant Census:
* ''Senna artemisioides'' subsp. ''alicia'' Randell (N.T., S.A., Qld., N.S.W.) has cylindrical petioles, the leaves with up to three pairs of flat, silky-hairy, egg-shaped leaflets at least wide and held vertically, exposing the lower surface. It has clusters of six to fifteen flowers with petals long, with ten fertile stamens and pods about long and wide.
* ''Senna artemisioides'' subsp. ''filifolia'', Randell commonly known as desert cassia, broom bush or punty bush, (W.A., N.T., S.A., Qld., N.S.W., Vic.) has cylindrical petioles that are more than long, the leaves with up to four pairs of cylindrical leaflets long. It has clusters of three to ten flowers with petals long, with ten fertile stamens and pods long and wide. Flowering mostly occurs in winter.
* ''Senna artemisioides'' subsp. ''helmsii'' (Symon) Randell (previously known as ''Cassia helmsii'' Symon) – commonly known as blunt-leaved cassia or crinkled cassia (W.A., N.T., S.A., Qld., N.S.W.) has cylindrical petioles, the leaves with flat, woolly-hairy, egg-shaped leaflets at least wide. It has clusters of four to ten flowers with petals long, with ten fertile stamens and pods long and wide. Flowering occurs in winter.
* ''Senna artemisioides'' subsp. ''oligophylla'' (F.Muell.) Randell – blunt-leaved cassia (W.A., N.T., S.A., Qld., N.S.W.) has cylindrical petioles long, the leaflets egg-shaped, long and wide. It has clusters of four to twelve flowers with petals long, with ten fertile stamens and pods about long and wide. Flowering occurs in winter.
* ''Senna artemisioides'' subsp. ''quadrifolia'' Randell (N.T., S.A., Qld.) has cylindrical petioles long, the leaflets narrowly elliptic, long and wide. It has clusters of four to eight flowers with petals long, with ten fertile stamens and pods about long and wide. Flowering occurs in winter.
* ''Senna artemisioides'' subsp. ''zygophylla'' (Benth.) Randell (S.A., Qld., N.S.W., Vic.) has cylindrical petioles, the leaves with flat, glabrous, linear to elliptic leaflets more than five times as long as broad. It has clusters of three to five flowers with petals long, with ten fertile stamens and pods long and wide. Flowering occurs in winter.

Four hybrid subspecies are also recognised by the Australian Plant Census:
* ''Senna artemisioides'' ( Gaudich. ex DC.) Randell subsp. × ''artemisioides'' (previously known as ''Cassia circinnata'' Benth.) (W.A., N.T., S.A., Qld., N.S.W., Vic.) has cylindrical petioles that are less than long, the leaves with three to eight pairs of cylindrical, hairy leaflets long, the edges rolled upwards so that the upper surface is not visible. It has clusters of four to twelve flowers with petals long, with ten fertile stamens and pods long and wide. Flowering mostly occurs in winter.
* ''Senna artemisioides'' subsp. × ''coriacea'' (Benth.) Randell (previously known as ''Cassia sturtii'' var. ''coriacea'' Benth.) (W.A., N.T., S.A., Qld., N.S.W., Vic.) has cylindrical petioles, the leaves flat with up to six pairs of linear to elliptic leaflets that are sparsely hairy and glaucous, the leaflet held horizontally. It has clusters of six to ten flowers with petals long, with ten fertile stamens and pods long and wide. Flowering occurs in winter.
* ''Senna artemisioides'' subsp. × ''petiolaris'' Randell – woody cassia (W.A., N.T., S.A., Qld., N.S.W., Vic.) has petioles that are laterally compressed. It has clusters of two to ten flowers with petals long, with ten fertile stamens and pods long and wide. Flowering usually occurs in winter.
* ''Senna artemisioides'' subsp. × ''sturtii'' Randell (previously known as ''Cassia sturtii'' R.Br..) (W.A., N.T., S.A., Qld., N.S.W.) has cylindrical petioles, the leaves flat with linear to elliptic leaflets that are densely silky- or woolly-hairy, but never glaucous. It has clusters of four to eight flowers with petals long, with ten fertile stamens and pods long and wide. Flowering occurs in winter.

A further two subspecies are named, but as of May 2023, not formally described:
* ''Senna artemisioides'' subsp. James Range (P.L.Latz 18528) NT Herbarium (N.T.)
* ''Senna artemisioides'' subsp. Kuyunba (B.Pitts 113) NT Herbarium (N.T.)

Distribution

Silver cassia is endemic to Australia, occurring in all mainland states and territories, and has been introduced to California, the Canary Islands, Cyprus, India, Iraq, Spain and Zimbabwe.

Ecology

''S. artemisioides'' is a recognized larval food plant for several species of butterfly and moth, including the small grass yellow, icilius blue, twig looper, blotched satin moth and bag-shelter moth. Seed dispersal is aided by ants which eat the arils.

Use in horticulture

''Senna artemisioides'' adapts to a wide range of climatic conditions, but is susceptible to frost, especially when young. It prefers dry, well-drained sites with full sun. As an ornamental plant, it is propagated readily from seed, which should first be briefly immersed in boiling water.

This species has gained the Royal Horticultural Society's Award of Garden Merit.

Images of subspecies

References

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artemisioides
Endemic flora of Australia
Flora of New South Wales
Flora of the Northern Territory
Flora of Queensland
Flora of South Australia
Rosids of Western Australia
Fabales of Australia
Garden plants of Australia
Drought-tolerant plants