Physostegia virginiana (L.) Benth.

Obedient plant

Physostegia virginiana plant

Family - Lamiaceae

Stems - To +1.5m tall, herbaceous, erect, 4-angled, glabrous, multiple from base, simple to branching above, hollow, often forming roots from nodes just above and at ground level, rhizomatous.

Physostegia virginiana stem

Leaves - Opposite, sessile, linear to linear-lanceolate, serrate(teeth with curved apices), acute to acuminate, glabrous, to 15cm long, 1.5cm broad, with prominent midrib.

Physostegia virginiana leavesPhysostegia virginiana leaves

Inflorescence - Single flowers from axils of small bracts forming a dense elongate spike to +40cm (in fruit). Axis of inflorescence dense pubescent. Flowers sessile or with a pedicel -1mm long. Subtending bracts sessile, lanceolate, acuminate, to +1cm long, (larger in fruit), dense pubescent.

Physostegia virginiana inflorescence

Physostegia virginiana inflorescence

Flowers - Corolla bilabiate, pinkish, pubescent externally. Corolla tube to +/-2.3cm long, constricted at base where surrounded by calyx, expanded beyond calyx. Upper lip 8-9mm long, 7-8mm broad, truncate to rounded at apex, the sides parallel. Lower lip 3-lobed. Lateral lobes 3-4mm long, 3mm broad. Central lobe 5-6mm long, 4-5mm broad, with purple spotting internally,(purple coloration extended into throat of corolla). Stamens 4, didynamous, ascending under the upper lip of the corolla. Filaments adnate for most of length(seemingly by dense pubescence), white or tinged with pink. Anthers purplish-brown, 1.7mm long. Style inserted between stamens (and slightly longer), white, glabrous, 2.5cm long. Stigma 2-lobed, filiform.Ovary 4-parted, green, glabrous. Calyx tube 6mm long(in flower), dense pubescent, pitted internally, 5-lobed. Lobes equal, acute, 2.2mm long(in flower). Calyx accrescent, to +1cm in fruit. Nutlets to +3mm long.

Physostegia virginiana calyxCalices.

Physostegia virginiana flowersFlowers.

Physostegia virginiana flowersMore pink flowers.

Flowering - May - September.

Habitat - Prairies, glades, wooded bluffs, streambanks, railroads.

Origin - Native to U.S.

Other info. - This is a popular and well known native plant. It is widely cultivated and used in butterfly and landscape gardens. The plant has many varieties in cultivation. A common name for the species is "Obedient Plant" because the plants flowers can be rotated or twisted to new positions and will remain this way and continue to grow.

Physostegia virginiana is highly morphologically variable and has been variously divided into varieties. Yatskievych mentions that assignment of infraspecific forms is often difficult due to extensive intergradation of characters, and the difficulty is compounded by presence of garden escapes which do not key well. Even differentiation from other species of Physostegia can be challenging.

Photographs taken at the Bethel Prairie Conservation Area, MO., 7-4-03 and off Hwy 80, Montgomery County, AL., 6-4-05.