Amsonia illustris Woods.

Shining Blue Star

Amsonia illustris plant2

Family - Apocynaceae

Habit - Perennial forb, sometimes woody near base.

Stems - Ascending to erect, to 1 m, usually multiple from base, sometimes branching near tips, with milky sap, glabrous.

Amsonia illustris stemStem and nodes.

Amsonia illustris sapSap of stem.

Leaves - Alternate, short-petiolate (becoming sessile near base of plant), simple, entire. Petioles to 1 cm long. Blades lanceolate to linear-lanceolate, sharply pointed, 12 cm long, 3 cm broad, shiny green and glabrous on upper surface, pale green and glabrous or sparsely hairy underneath.

Amsonia illustris leavesLeaves.

Amsonia illustris leaves2Glossy leaf upper sides.

Inflorescence - Terminal clusters, roughly cylindrical to hemispherical, 4-6 cm long at flowering, positioned above the leaves. Flower stalks 8-10 mm long, often tinged with blue.

Amsonia illustris inflorescenceInflorescence.

Flowers - Calyces 5-lobed, sparsely hairy, the lobes 1.0-1.2 mm long, triangular. Corollas 5-lobed, densely hairy internally, glabrous externally, the tube 6-7 mm long, about 1 mm wide at base, the throat 2.0-2.4 mm wide, the lobes 5-8 mm long, 1.5-2.5 mm wide, narrowly oblong to linear-lanceolate, light blue. Stamens 5, alternating with corolla lobes, adnate to corolla tube near apex. Anthers yellow-orange, 1 mm long. Style glabrous, 5 mm long. Stigma capitate, winged at base. Carpels 2.

Amsonia illustris calyxCalyx and corolla tube.

Amsonia illustris flowerCorolla.

Amsonia illustris flowersCorollas.

Fruits - Slender follicles to 12 cm long, terete, many seeded, glabrous, drooping at maturity, positioned among the leaves, slightly constricted between the seeds and sometimes breaking between them. Seeds 6-9 mm long, 2-3 mm wide, the surface usually with low, corky ridges and tubercles, dark brown.

Flowering - April - May.

Habitat - Rocky ground along bluffs and streambanks, gravel bars, occasionally glades.

Origin - Native to U.S.

Other info. - This plant is quite striking when in flower and is gaining popularity as a cultivated ornamental. The shiny green leaves and dense flower clusters are very attractive, and the slender pods add interest in the autumn. In Missouri it is generally found south of the Missouri River and in the western 2/3 of the state. Another species, A. tabernaemontana Walt., looks similar but has duller leaves which are also slightly broader, glabrous calyces, and fruits borne erect. A. illustris has been viewed as a variety of A. tabernaemontana, though the characters listed above and the habitat preferences seem to be consistent differences.

Photographs taken at Schumaker Park, Jackson County, MO., 5-12-00, and in Ripley County, MO., 5-15-04 (DETenaglia); also at Shaw Nature Reserve, Franklin County, MO, 4-29-2007 and 5-23-2008; and on gravel bars in the Meramec River, Crawford and St. Louis Counties, 4-18-2012 and 5-4-2012 (SRTurner).


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