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Electronic Flora of South Australia species Fact Sheet

Family: Leguminosae
Swainsona oroboides

Citation: F. Muell. ex Benth., Fl. Aust. 2:222 (1864).

Synonymy: S. behriana F. Muell. ex J. Black, Trans. R. Soc. S. Aust. 51:379 (1927); S. reticulata J. Black, Fl. S. Aust. 320 (1924); S. oroboides F. Muell. ex Benth. subsp, reticulata (J. Black)A. Lee, Contr. N.S.W. natn. Herb. 1, 4:198 (1948); S. tenuis E. Pritzel in Diels & E. Pritzel, Bot. Jb. 35:270 (1904); S. oroboides F. Muell. ex Benth. var. hirsuta J. Black, Fl. S. Aust. 320 (1924); S. oroboides F. Muell. ex Benth. Subsp. hirsuta (J. Black)A. Lee, Contr. N.S.W. natn. Herb. 1, 4:200 (1948); S. oroboides F. Muell. ex Benth. Subsp. sericea A. Lee, Conlr. N.S.W. natn. Herb. 1, 4:201 (1948); S. sericea (A. Lee)H. Eichler, Suppl. 193 (1965).

Common name: Variable swainson-pea (or swainsona), kneed Darling pea.

Description:
Mostly small prostrate or ascending plants, often with a short woody rootstock; stems radiating, 5-10 sometimes to 30 cm long; indumentum variable in density, mostly of basifixed hairs often attached laterally, sometimes having a small tubercle at the base, more or less appressed to asymmetrically medifixed, long silvery to curved bristly or distinctly pointed at both ends, on stems, leaves and peduncle; leaves 2-12 cm long, with 5-17 leaflets; leaflets narrow-lanceolate to narrow-oblanceolate, narrow-elliptic to narrow-obovate, in some specimens the terminal (10-50 x 4-6 mm) distinctly longer, the laterals 9-40 mm long and flaccid, or mostly the terminal leaflets hardly longer than the adjacent, 3-25 x 1-3 mm, acute or obtuse rarely truncate, pubescent on both sides but less so above to glabrescent; stipules linear to broad-lanceolate, 2-10 mm long.

Flowers 7-9 mm long on pedicels 0.5-4 mm long and with hairs similar to those on the calyx; peduncles to 15 usually 5-9 cm long, with 3-5 (rarely to 10) flowers in terminal short racemes or subumbellate; bract lanceolate or broad-lanceolate, usually shorter than the pedicel, hoary, scarious; bracteoles at the base of the calyx, ovate to subulate, to 0.5 mm long; calyx 4-7 mm long, pubescent with light and/or dark hairs more or less dense and spreading to slightly appressed; teeth triangular or lanceolate to acuminate, usually shorter than the tube; petals bluish, purple or red; standard broadly ovate, shallowly notched, usually a little longer than broad, obliquely veined, often with 2 yellowish-green blotches centrally, without any calli or with 2 more or less poorly developed parallel vertical ridges above the rather broad but short to 2.5 mm long claw; wings as long as the keel, ovate-oblong, with an auricle above the bent claw; keel triangular-obovate, obtuse, with or without a pair of folds near the auricles, claw 2-3 mm long; ovary on a gynophore c. 1 mm long, fusiform, densely pubescent with appressed hairs; style slender, slightly flattened in the lower half, bearded for all its length, gradually attenuated into a geniculate tip, abruptly inflexed almost at right angles to the rest of the style, tip pubescent on the ventral side, glabrous dorsally, without any ring or hairtufts behind the stigma.

Pod ovoid and 8-20 x 5-9 mm or cylindrical and 10-20 x 2-5 mm, suture impressed, smooth or reticulate with raised nerves, pubescent with spreading or appressed hairs, to 20-seeded; seed cordate, c. 1.7 mm long, olive-green to brown.

image of FSA2_Swainsona_oro.jpg
Image source: fig. 338A in J.P. Jessop and H.R. Toelken Ed. 1986. Flora of South Australia (4th edn).

Published illustration: Williams (1984) Native plants of Queensland 2:275.

Distribution:  Scattered throughout sandy soils, loamy earths or heavy clay, in flood-plains or gibber-plains.

S.Aust.: NW, LE, GT, EP, MU.   W.Aust.; N.T.; Qld; N.S.W.; Vic.

Conservation status: native

Flowering time: July — Oct., sometimes after good rains in summer.


SA Distribution Map based
on current data relating to
specimens held in the
State Herbarium of South Australia

Biology: The number of intermediates is much greater in the present larger collections than seen by A. Lee. The lack of pods in most of the specimens and the indistinct characters among the types prevents a justifiable segregation into subspecies, although a big variation in the species is obvious. The intergradation and the distribution pattern of the variants is not correlated, and no workable key could be produced. As A. Lee has widely commented on intergradations between subspecies, I am convinced that the subspecies should be treated as synonyms.

Taxonomic notes: A. Lee (1948) formed 4 subspecies as follows.

1. Leaflets 5-7, the terminal leaflet distinctly longer than the laterals, appressed-pubescent below and glabrous above to more densely spreading-pubescent on both sides with basifixed or subbasifixed hairs, always acute; calyx pubescent with appressed, short, pale hairs or with more loosely appressed to spreading, longer, shining or dark-coloured hairs; fruit ovoid, 8-10 mm long, 5-9 mm in diam., the suture intruded about one-fourth of the diameter .... subsp. oroboides.

1. Leaflets 5-13 (usually more than 9), the terminal not much longer than the laterals; fruit cylindrical, 10-20 mm long, 2-5 mm in diam., the suture intruded to the base.

2. Hairs of the pubescence rather long, more or less medifixed; pubescence dense and silvery to very sparse; leaflets usually 9-11, oblanceolate or narrower to narrow-elliptic, the apex acute; inflorescence shortly racemose, the calyx with mixed dark-grey and light hairs .... subsp. sericea.

2. Hairs of the pubescence basifixed or laterally attached at the base, the pubescence rather dense to sparse, occasionally silvery.

3. Leaflets 7-17, usually 9-11, pubescent with loosely appressed to curved-spreading hairs on both sides, oblanceolate or broader, to narrow-oblong or cultrate; inflorescence shortly racemose, the calyx brown- or white-pubescent or with mixed hairs, the teeth equal to the tube .... subsp. reticulata.

3. Leaflets 7-13, lanceolate or narrower, sparsely hirsute with curved-spreading hairs on both sides, those on the upper surface pointing inwards and towards the apex; inflorescence umbellate, the calyx pubescent with dark-brown hairs, the teeth about equal to the tube .... subsp. hirsuta.

Key to Infraspecific taxa:
1. Leaflets 5-7, the terminal leaflet distinctly longer than the laterals, appressed-pubescent below and glabrous above to more densely spreading-pubescent on both sides with basifixed or subbasifixed hairs, always acute; calyx pubescent with appressed, short, pale hairs or with more loosely appressed to spreading, longer, shining or dark-coloured hairs; fruit ovoid, 8-10 mm long, 5-9 mm in diam., the suture intruded about one-fourth of the diameter
subsp. oroboides.
1. Leaflets 5-13 (usually more than 9), the terminal not much longer than the laterals; fruit cylindrical, 10-20 mm long, 2-5 mm in diam., the suture intruded to the base
 
2. Hairs of the pubescence rather long, more or less medifixed; pubescence dense and silvery to very sparse; leaflets usually 9-11, oblanceolate or narrower to narrow-elliptic, the apex acute; inflorescence shortly racemose, the calyx with mixed dark-grey and light hairs
subsp. sericea.
2. Hairs of the pubescence basifixed or laterally attached at the base, the pubescence rather dense to sparse, occasionally silvery
 
3. Leaflets 7-17, usually 9-11, pubescent with loosely appressed to curved-spreading hairs on both sides, oblanceolate or broader, to narrow-oblong or cultrate; inflorescence shortly racemose, the calyx brown- or white-pubescent or with mixed hairs, the teeth equal to the tube
subsp. reticulata.
3. Leaflets 7-13, lanceolate or narrower, sparsely hirsute with curved-spreading hairs on both sides, those on the upper surface pointing inwards and towards the apex; inflorescence umbellate, the calyx pubescent with dark-brown hairs, the teeth about equal to the tube
subsp. hirsuta.

Author: Not yet available


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