Swainsona

Taxonomy

Swainsona R.A. Salisbury Parad. Lond. ad t. 28. 1 Mar 1806.

Subfamily: Faboideae.
Phylogenetic Number: 3.16.02.
Tribe: Galegeae.
Subtribe: Coluteinae.
Species Studied - Species in Genus: 15 studied; 85 in genus.

Description

Fruit: A legumelegume:
usually dry, dehiscent fruit derived from a single carpel that opens along two longitudinal sutures
; unilocular, or bilocular (see also Astragalus (16.14)); at least 1–5 cm long; 0.3–2.5 cm wide; 0.1–0.35 cm thick; 2–9 times longer than wide, or more than 9 times longer than wide; with persistent androecial sheath, or deciduous androecial sheath; with deciduous corolla; with persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight, or curved (slightly); not plicate; not twisted; asymmetrical, or symmetrical; linear, or oblong, or elliptic, or falcate; with both sutures parallelly curved, or both sutures nearly straight; not inflated, or inflated; flattened; with beak; straight, or declined; with solid beak the same color and texture as fruit; short tapered at apex, or rounded at apex; aligned with longitudinal axis of fruit, or oblique with longitudinal axis of fruit, or right-angled with longitudinal axis of fruit; short tapered at base; right angled with longitudinal axis of fruit, or oblique with longitudinal axis of fruit; with the apex and base uniform in texture; membranous, or coriaceous, or ligneous; seed chambers externally invisible; margin not constricted; margin without sulcus; margin plain; wing(s) absent; stipitate, or substipitate, or nonstipitate; with the stipe at least up to 10 mm long; indehiscent, or with all layers dehiscing (to tardily dehiscent); splitting along suture(s). Dehiscence of valves along 1 suture; medial and up and down; passive. Replum invisible. Epicarp dull; monochrome; brown; with surface texture uniform; glabrous, or pubescent and indurate; with hairs erect; with 1 type of pubescence; villous; with pubescence gray; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases plain; eglandular; without spines; not smooth; with elevated features; veined; reticulately veined and transversely veined relative to fruit length; not tuberculate, or tuberculate (bases of hairs); wrinkled, or tuberculate; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp absent. Endocarp present; visible; dull; opaque; monochrome; tan; smooth; without adhering pieces of testa; nonseptate; chartaceous; not exfoliating; remaining fused to epicarp; without wings; entire. Seed(s) few to numerous; length parallel with fruit length (assumed); assumed overlapping; in 2 or more series. Funiculus 0.5–2 mm long (at least); of 1 length only; filiform; S-curved. Aril present; dry; when dry rim-aril; entire; white.

Seed: 3.5–4 mm long; 3–3.5 mm wide; 1 mm thick; not overgrown; not angular; asymmetrical; reniform; compressed; with surface smooth; with visible radicle and cotyledon lobes; with external groove between radicle and cotyledon lobes; with external groove between radicle and cotyledon lobes same color as testa; without hilar sinus, or with deep hilar sinus; without umbo on seed faces; without medial ridge on each face. Cuticle not exfoliating; not inflated; not wrinkled. Testa present; without pieces of adhering epicarp; not adhering to endocarp; free from endocarp; dull; not modified by a bloom; colored; monochrome; reddish brown; glabrous; not smooth, or smooth; with elevated features; reticulate; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; partially concealed, or fully concealed; concealed by radicle lobe; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; punctiform; between cotyledon and radicle lobe; flush; within halo, or not within corona, halo, or rim; halo lighter than testa. Lens discernible; 0.5 mm long; with margins straight; linear; not in groove of raphe; confluent with hilum; mounded; dissimilar color from testa; darker than testa; black; not within corona, halo, or rim, or within halo; halo color lighter than testa. Endosperm present; thick; not pluglike and not resembling tip of radicle; covering entire embryo; adnate to embryo. Cotyledons smooth; outer face of one cotyledon flat and other cotyledon convex; both the same thickness; both more or less of equal length; not folded; margin entire 180 degrees from base of radicle; similar at apex; not concealing radicle; entire over radicle; without lobes; with the interface division terminating at base of radicle; without margins recessed; tan; inner face flat; glabrous on inner face. Embryonic axis deflexed; oblique to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; bulbose; lobe tip straight, or hooked; deflexed and parallel to cotyledon length; centered between cotyledons; 1/2 to nearly length of cotyledons. Plumule rudimentary; glabrous.

Distribution

Australia (Most species) and southern New Zealand (S. novae-zelandiae J.D. Hooker).

Old World; Australia to New Zealand (S. novae-zelandiae J.D. Hooker in New Zealand).

Generic Notes

Thompson (1993) monographed Swainsona and recognized 85 species, the count that we used. Although fruits are seldom collected for most species, the fruits have great phylogenetic and diagnostic significance for the species. Thompson regarded the primitive and most unmodified fruits to be greatly inflated with seeds that are "erratic in their maturing into viable seeds." She also noted that "seeds have proved difficult to study, few being available in the mature state and those seeming to be somewhat inconsistent in size, shape, surface sculpturing and colour." Species of Swainsona, containing swainsonine, are a well known cause of livestock poisoning. Swainsona in Australia has many parallels with Astragalus (16.15) in North America. Thompson transferred Clianthus (16.01) formosus (G. Don) N.C. Ford & J.W. Vickery to Swainsona. Heenan (1998c) carried out phylogentic analyses of the Carmichaelia (17.05) complex, Clianthus, and 13 species of Swainsona, including S. novae-zelandiae J.D. Hooker. He concluded that "Swainsona is polyphyletic if S. novae-zelandiae is included," and recommended the segregation of S. novae-zelandiae as a monotypic genus. The genus Montigena P.B. Heenan (Heenan, 1998b) was established with the single New Zealand species M. novae-zelandiae (J.D. Hooker) P.B. Heenan. Wagstaff et al. (1999) carried out phylogenetic analyses of the same genera using DNA data. Their consensus phylogenetic trees showed M. novae-zelandicae as deeply within the clade with most of the Swainsona species contradicting the findings of Heenan (1998). We have chosen to include M. novae-zelandiae in Swainsona pending an expression of a consensus opinion on the status of Montigena by the taxonomic community.

Tribal Notes

Tribe Galegeae

Traditionally this tribe has been called Galegeae. Reveal (1997) reported that the name Astragaleae was published before the name Galegeae. Following the International Code of Botanical Nomenclature (Greuter et al., 1994), the oldest name for a taxon must be used, so Reveal suggested that this tribe should be called Astragaleae. In 1999 Reveal (1999) reversed himself, so that this tribe remains the Galegeae. Welsh (1960) reported on the Galegeae of north-central United States. Sanderson and Liston (1995) carried out cladistic analyses of Galegeae genera using molecular data. They concluded that Galegeae is paraphyletic having given rise to tribes Cicereae (20), Hedysareae (18), Trifolieae (21), and Fabeae (19), and therefore requiring a re-evaluation of the circumscription of Galegeae. Heenan (1995, 1998c), utilizing unpublished nuclear ribosomal DNA ITS data, concluded that "Carmichaelia (17.05) is nested within (the) 'Astragalean clade' of Galegeae" and is the sister group of Clianthus. He therefore supported the proposal of Sanderson and Wojciehowski (1996) that Carmichaelieae should not be recognized at tribal level, but rather included in Galegeae.