Securigera varia (L.) Lassen (crown vetch)
Coronilla varia L.
Pl. 406 g–i;
Map 1801
Plants perennial herbs, with a woody
taproot below a short, branched caudex. Stems 30–120
cm long, spreading to loosely ascending or occasionally ascending, branched,
often forming loose mats or mounds, angled or ridged, unarmed, glabrous or
sparsely pubescent with spreading hairs. Leaves alternate, odd-pinnately compound with 9–25 leaflets, sessile or nearly
so, the rachis 5–12 cm long. Stipules 1–4 mm long, narrowly lanceolate
to narrowly oblong or oblong-triangular, usually reflexed, often with a green central
stripe and pale margins, rounded to bluntly or sharply pointed at the sometimes
darkened tip, the margins entire or with a few minute teeth (rarely with a
single basal lobe); stipels absent. Leaflets 6–25 mm
long, 2.5–9.0(–12.0) mm wide, the terminal leaflet usually narrowly oblanceolate to oblong-oblanceolate,
the lateral leaflets oblong to oblong-oblanceolate,
the shortest ones sometimes oblong-obovate, rounded
or angled at the base, rounded to truncate or broadly and bluntly pointed at
the tip, the midvein extended as a minute, sharp
point at the very tip, the margins entire, the surfaces glabrous, the upper
surface usually with microscopic, dark purple gland-dots (visible only under
magnification), the undersurface often purplish-tinged or -mottled.
Inflorescences axillary, umbellate to loosely headlike
clusters of (5–)10–15(–20) flowers, the stalk 5–15 cm
long, usually with sparse, short, spreading hairs, the tip with 1 bract per
flower, these 0.5–1.0 mm long, linear to narrowly oblong or rarely forked
apically, darkened at the tips, persistent, each flower with a stalk 3–7 mm
long above the bract; bractlets absent. Calyces
glabrous, the tube 1.0–1.5 mm long, broadly bell-shaped to hemispheric, more or
less 2-lipped, the upper 2 lobes fused most of their length, 0.7–1.0 mm long,
the unit broadly triangular with a forked tip, the lower 3 lobes 0.5–1.0 mm
long, more or less similar, broadly triangular, the margins often thin and
pale, glabrous or occasionally minutely and finely hairy, mostly in the sinuses
between the lobes. Corollas papilionaceous, pink to
purple, sometimes appearing bicolorous, the banner
sometimes with a darker, small keel, the wings often lighter (sometimes nearly
white), the keel dark purple toward the tip, the banner 9–13 mm long, 5–8 mm
wide, the expanded portion broadly ovate, abruptly arched upward from below the
midpoint, the wings 9–15 mm long, 4–5 mm wide, oblong, the keel 10–12 mm long,
2–4 mm wide, boat-shaped, fused to the tip, abruptly curved upward near the
midpoint, narrowed or tapered to a bluntly pointed tip. Stamens 10, all of
similar lengths, 9 of the filaments fused and 1 usually shorter filament free,
the fused portion 6–7 mm long, the free portion 3–4 mm long, curved upward, the
anthers small, attached at the base, yellow. Ovary 5–7 mm long, the style 5–6
mm long, slender, curved upward, glabrous, the stigma small and terminal.
Fruits loments, 2–6 cm long, 1.5–2.2 mm wide, narrowly oblong to more commonly
linear, short-stalked, tapered to a slender, beaked tip, bluntly 4(5)-angled,
only very slightly constricted between the seeds, green to straw-colored or
tan, glabrous, breaking apart at maturity into 3–12, 1-seeded segments, these
indehiscent or sometimes dehiscing more or less longitudinally with age. Seeds 3–4 mm long, 0.9–1.5 mm wide, more or less cylindric (bluntly rectangular in outline), the surface
reddish brown, smooth, dull. 2n=24.
May–August.
Introduced, scattered nearly throughout
the state, though as yet uncommon or absent from portions of the Glaciated
Plains and Mississippi Lowlands Divisions (native of Europe, Asia; introduced
nearly throughout the U.S. [including Hawaii] and Canada). Banks of streams and
rivers, margins of ponds and lakes, glades, and openings of mesic
to dry upland forests; also pastures, old fields, old strip mines, railroads,
roadsides, and open, disturbed areas.
Securigera varia is identified by the sprawling habit, pinnately compound leaves, umbellate inflorescence of
pinkish flowers on a long stalk, and narrow, linear loments that break up into
segments. Until recently, crown vetch was planted widely for erosion control,
especially along highways following construction work. This practice has been
discouraged, because although the plants form dense masses covering the ground,
on steep slopes they frequently hide rather than eliminate soil erosion.
Additionally, there have been concerns about the aggressive spread of the
species into neighboring native plant communities, particularly along
drainages. Invasive populations have been recorded in side-drainages of Ozark
streams and rivers at points some 5 kilometers from the nearest road crossing.
Securigera varia provides cover for small mammals and birds. It is eaten
by animals and has sometimes been cultivated for fodder. However, there are
concerns about low-level toxicity to livestock from nitrotoxins
(Burrows and Tyrl, 2001).