Justicia americana (L.) Vahl

Water Willow

© SRTurner

Family - Acanthaceae

Habit - Rhizomatous perennial forb, often semi-aquatic, often densely colonial.

	Roots and rhizome.
© SRTurner

Stems - Ascending to erect, to 1.0 m, often rooting at lower nodes, glabrous. Cross section shows seven distinct vascular bundles arranged in a hexagonal array with one bundle at the center.

	Stem and node.
© SRTurner

Leaves - Opposite, sessile to very short-petiolate, 1-16 cm long, the lowermost leaves often reduced, mostly narrowly elliptic or lanceolate, rarely broader, tapered at the tip and base, glabrous.

	Leaf adaxial.
© SRTurner

	Leaf abaxial.
© SRTurner

Inflorescence - Axillary headlike clusters, the inflorescence stalk slightly shorter than to longer than the subtending leaf.

	Inflorescences.
© SRTurner

	Inflorescence.
© SRTurner

	Inflorescence.
© DETenaglia

Flowers - Calyces 4-8 mm long, the lobes narrowly lanceolate. Corollas 8-15 mm long, strongly bilabiate, the lower lip 3-lobed, white or pale purple with purple markings, the upper lip reflexed, apically notched, usually light purple, rarely white. Stamens 2, adnate near apex of corolla tube, slightly exserted from upper lip. Filaments white, 5 mm long, glabrous. Anthers with distinct sacs, purplish to brownish. Ovary green, glabrous, 1.2 mm long, conic. Style white, glabrous, 9 mm long.

	Calyces.
© SRTurner

	Flower.
© DETenaglia

	Flowers.
© SRTurner

	Flowers.
© SRTurner

Fruits - Capsules 8-13 mm long, club-shaped from a narrow base. Seeds 2.0-3.5 mm long, reddish brown to brown, lacking a differentiated margin, the surfaces papillose.

	Developing fruit.
© SRTurner

Flowering - May - October.

Habitat - Usually emergent aquatics along banks of streams, less commonly margins of ponds and sloughs, ditches.

Origin - Native to the U.S.

Lookalikes - Justicia ovata, which is uncommon in Missouri.

Other info. - This plant forms large mats or colonies near the shorelines of lakes, ponds and streams throughout most of Missouri except for the northwestern corner of the state. It is found in most of the eastern half of the continental U.S. The plant is easily recognized by its narrow, opposite leaves, unusual flowers, and aquatic habitat. Although the flowers have distinct purplish markings, they still look whitish from a distance.

Photographs taken at the Kansas City Zoo, 6-13-00, and along the shores of the Current River, Shannon County, MO., 6-13-03 (DETenaglia); also in Washington, Franklin County, MO, 6-6-2019 (SRTurner).