Pickerel Weed

Found in Marshy places, rice fields, from plains up to 1550 m but not common in our area. The vegetative parts of the plant vary in size and shape; the flowers are ephemeral (Backer and Heemstede, l.c.). Parts of the plants are used as a vegetable; root is chewed to cure toothache; bark used medicinally for asthma.

By the 1970s, Monochoria vaginalis had become part of the rice-field flora of California (S. C. H. Barrett and D. E. Seaman 1980). C. D. K. Cook (1989) described this species as characteristic of rice fields; however, no records are known from the rice fields of Missouri to Louisiana.

As is typical of many aquatic annuals, plant size, leaf shape, and flower number are highly variable in relation to the amount of water (C. D. K. Cook 1989). Specimens from California typically have three to eight flowers, while descriptions of those from other parts of the world (H. Aston 1977; C. D. K. Cook 1989) suggest that the inflorescences of this species may have up to 20 flowers.

The stems and leaves are used as a vegetable.

Rootstock small with adventitious roots. Stem suberect to erect. Leaves 25-70 x 11-39 mm, with 4-21 cm petiole; ovate to ovate-lanceolate, acute to acuminate, base rounded to cordate; nerves convergent. Inflorescence soon deflexed. Pedicel c. 7 mm long. Flowers buds lilac-blue. Perianth blue, spotted red, 8-8.5 mm long, oblong, subacute. Stamens c. half as long as the perianth. Ovary ovoid, 3 mm long; style c. 2 mm long, stigma 3-lobed. Capsule ovoid, c. 1 cm long. Seeds 1 mm long, elongated, ribbed longitudinally, transversely striated.

Flowering stems 8–16.5 cm, distal internode 3–15 mm. Sessile leaves up to 5 cm, blade linear, apex acuminate. Petiolate leaves: stipule 3.5–5.7 cm; petiole 7–28 cm, rigid; blade cordate, 4–8 × 1.8–5.2 cm. Inflorescences paniculate, 3–8-flowered, all flowers opening same day; spathes 1.9–4 cm, sometimes with lanceolate to ovate extension. Perianth: limb lobes blue or white, narrowly ovate, 10–14 mm; larger stamen with hook, 4–6 mm, shorter stamens 3–4 mm; filaments linear, glabrous; style glabrous. Seeds 10–11-winged, 0.8–1.2 × 0.4–0.6 mm.

Herbs aquatic. Stems erect or obliquely so. Radical leaves with broad sheath; petiole 3--50 cm; leaf blade narrowly cordate, broadly or narrowly ovate, or lanceolate, 2--21 × 0.8--10 cm, apex acute to acuminate. Flowering stems 12--35 cm. Inflorescences soon reflexed after anthesis, 3--8(--12)-flowered; peduncle 1--3 cm, base bracteate; bract lanceolate. Flowers pedicellate. Perianth segments purplish, ovate-lanceolate to oblong, 0.8--1.5 cm. Larger stamen: filament appendaged; anther 1.8--4 mm. Smaller stamens: filaments filiform; anthers 1.5--3 mm. Capsule ovoid to ellipsoid, 0.7--1 cm. Seeds ellipsoid, ca. 1 mm; wings 8--12. Fl. Aug--Sep, fr. Sep--Oct.

Distribution: SE Asia to China, Japan and throughout Malaysia.

Throughout China [Bhutan, Cambodia, India, Indonesia, Japan, Korea, Laos, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Russia (Siberia), Sri Lanka, Thailand, Vietnam; Africa, Australia].

Himalaya (Nepal, Bhutan), India east to China & Japan, Malaysia.

introduced; Calif.; Asia (India, China, Japan, and Malayan Islands).

200-1800 m

Fl. Per.: July-November.

Flowering (Jul--)Sep--Oct.

Rice fields, ephemeral ponds; 0--200m.

Rice fields, ditches, ponds, swamps; near sea level to 1500 m.

Pontederia vaginalis N. L. Burman, Fl. Indica 80. 1768; Boottia mairei H. Léveillé; Monochoria linearis (Hasskarl) Miquel; M. ovata Kunth; M. vaginalis var. pauciflora (Blume) Merrill; M. vaginalis var. plantaginea (Roxburgh) Solms; P. linearis Hasskarl; P. ovata Hooker & Arnott (1837), not Linnaeus (1753); P. pauciflora Blume; P. plantaginea Roxburgh.

Pontederia vaginalis Burman f., Fl. Indica, 80. 1768; Monochoria plantaginea (Roxburgh) Kunth; Monochoria vaginalis var. pauciflora (Blume) Merrill

Monochoria vaginalis is a species of flowering plant in the water hyacinth family known by several common names, including heartshape false pickerelweed and oval-leafed pondweed.

It is native to much of Asia and across many of the Pacific Islands, and it is known in other areas as an introduced species. It is often an invasive noxious weed, and is listed on the United States Federal Noxious Weed List. An aquatic plant, it is invasive in rice paddies and other water bodies. This is an annual or perennial herb growing in water from a small rhizome. It is quite variable in morphology. The shiny green leaves are up to about 12 centimeters long and 10 wide and are borne on rigid, hollow petioles. The inflorescence bears 3 to 25 flowers which open underwater and all around the same time. Each has six purple-blue tepals just over a centimeter long. The fruit is a capsule about a centimeter long which contains many tiny winged seeds.