Myagrum perfoliatum L. Annual, taprooted, in range rosetted (including at flowering), 1–stemmed at base, erect with spreading–ascending lateral branches in canopy, in range 25—60 cm tall; shoots with basal leaves and cauline leaves, on robust plants 20+ basal with some withered at flowering, cauline leaves clasping and partially fused to stem with basal lobes free on back side of node, amplexicaul), basal leaves mostly pinnately lobed or sometimes with cut margins (runcinate) and easily wilted, glabrous, especially cauline leaves grayish green and glaucous.
Stems nearly cylindric, to 10 mm diameter, pale green, slightly zigzagged, internodes to 25 mm long, epicuticular wax persisting mostly beneath bases of petioles.
Leaves helically alternate, pinnately lobed and subsessile (basal leaves) and unlobed and sessile with backward–pointing basal lobes (auriculate cauline leaves), without stipules; blade of basal and lower cauline leaves mostly lobed but sinuses not reaching midrib (dandelion–like, Taraxacum), oblanceolate to oblong, to 220 × 55 mm, with conspicuous, fleshy, white midrib base–to–tip, base of blade indistinct from petiole having winglike green blade tissue several mm wide for1/4 of blade, lobes often paired but subopposite, broadly triangular, subentire to having low teeth, terminal lobe broadly elliptic, pinnately veined with midrib shallowly channeled on upper surface and strongly raised on lower surface with slightly raised lateral veins, lower surface usually glaucous; blade of middle and upper cauline leaves oblong–elliptic or elliptic to narrowly arrow–shaped, to 105 × 30 mm decreasing upward, with obtuse basal lobes (auricles) and free portions sometimes overlapping on back side of stem, auricles to 14 mm long, blade subentire to entire and wavy on margins, acute (acuminate) at tip, with midrib slightly raised on lower surface.
Inflorescence raceme, terminal on principal shoots, the larger racemes 30+–flowered, flat–topped and ca. 10 mm across at tip, with rachis elongating in fruit, lacking bracts, glabrous and somewhat glaucous; bract subtending raceme = diminutive upper cauline leaf; peduncle cylindric, initially < 2 mm long increasing to 12 mm long in fruit; bractlet subtending pedicel absent; pedicel ascending becoming erect and often appressed in fruit, cylindric, 2—2.5 mm long increasing 2× in fruit, light green.
Flower bisexual, ± radial, 3—3.5 mm across; sepals 4, in range ovate and the outer 2 slightly saclike at base, 1.9—2.4 × 0.8—1.2 mm, light yellow with light green, acute to rounded at tip; petals 4, oblanceolate (claw not distinct), in range 2.9—3.8 × 0.7—1 mm, erect portion (“claw”) pale yellow and spreading portion light yellow, rounded at tip; stamens 6, free, dimorphic, outer 2 short and inner 4 longer, with anthers of longer stamens at level of stigma; filaments 2.3—2.6 mm long (short stamens) and ca. 3.5 mm long (long stamens), whitish at base to light yellow above midpoint; anthers dorsifixed, dithecal, arrow–shaped, 0.7—0.8 mm long, light yellow, longitudinally dehiscent; pollen light yellow; pistil 1, ca. 3 mm long, glabrous; ovary superior, narrowly obovoid, ca. 1.6 × 0.6 mm, green, oddly 2–chambered with 2 ovules in a lower chamber (“augustiseptate”); style 4–sided, 0.35—0.4 mm long, light green, with a slightly domed, terminal stigma, stigma greenish and short–papillate.
Fruit siliqua (silicle), dehiscent, 1(—2)–seeded, somewhat heart–shaped with a pair of bulging shoulders, ca. 6—7 × 6—7 mm + a persistent beak (style) to 1 mm long, glabrous, seed only in lower chamber.
Seed oblong, 2—3 × 1—1.6 mm, brown.
A. C. Gibson