Indian Toothcup

Rice fields. 300-1800 m alt. Not common.

The species is closely associated with rice cultivation. There are unbranched plants with flowers sessile at nodes of the main stem that do not form lateral spikelike inflorescences. Cook (1979) found that although the unbranched form was sometimes genetically fixed, in many geographically scattered populations it was not fixed but ecologically induced as a result of crowded growing conditions.

Annual herb, erect, 10-19 cm tall, glabrous. Leaves obovate, obtuse, attenuate at the base, margin prominently cartilaginous, 5-13 mm long. 2-7 mm broad. Spikes axillary, in every axil, 4-9 mm long. Bracts leaf-like. Bracteoles subulate. Flowers 4-merous, 2-3 mm long. Hypanthium tubular-campanulate, membranous in fruit. Sepals 0.5-1 mm long, 1 mm broad, very acute. Petals minute, shorter than sepals. Ovary oblong. Capsule ± equalling the hypanthium, much shorter than the calyx. Seeds longer than broad.

Herbs, annual, terrestrial or amphibious, to ca. 40 cm. Stem creeping and branched at base, ascending, or erect, terete to weakly 4-angled. Leaves decussate, obovate-elliptic or obovate-oblong, 5-17 × 3-8 mm, base cuneate, margin translucent to opaque, white cartilaginous, apex obtuse. Bracts like foliage leaves or distinctly smaller on axillary spikes. Flowers in axillary spikes or sessile in bracts on main stem; bracteoles linear, reaching sepals or longer. Floral tube 4-merous, pink-red at anthesis, narrowly to broadly campanulate, 1.5-2.5 mm, 4-angled; sepals 4, lanceolate-deltate; epicalyx absent. Petals 4, pink, minute to ca. 1/2 as long as sepals. Stamens 4; anthers reaching sinus of sepals. Ovary ellipsoidal; style ca. 1/2 as long as ovary, slightly exserted. Capsule ellipsoidal, ca. 1 mm in diam., slightly exserted, 2-valved. Seeds ca. 0.4 mm. Fl. Sep-Oct, fr. Oct-Apr. 2n = 32*.

W. Asia, Himalaya, India east to China, Amur, Japan, Malaysia.

Distribution: Russia, Iran, Afghanistan, Pakistan, India, Malaya, China and Japan.

200-1400 m

Fl. Per.: August.

Wet places, paddy fields. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangsu, Jiangxi, Shanxi, Sichuan, Taiwan, Yunnan, Zhejiang [Bhutan, Cambodia, India, Indonesia, Japan, Korea, Laos, Malaysia, Myanmar, Nepal, Philippines, Sri Lanka, Thailand, Vietnam; C Asia; introduced in rice fields in Africa (Congo), Europe (Italy, Portugal), and North America (United States)].

Peplis indica Willdenow, Sp. Pl. 2: 244. 1799; Ameletia indica (Willdenow) Candolle; A. uliginosa Miquel; Rotala densiflora (Roth) Koehne var. formosana Hayata; R. elatinomorpha Makino; R. indica var. koreana Nakai; R. indica var. uliginosa (Miquel) Koehne; R. koreana (Nakai) Mori; R. uliginosa (Miquel) Nakai.

Rotala indica is a species of flowering plant in the loosestrife family known by the common name Indian toothcup. It is native to Southeast Asia. This aquatic plant is best known as a popular aquarium plant and as a weed of rice fields. It is known as an introduced species and a weed in rice-growing regions in Congo, Italy, and Portugal, and California and Louisiana in the United States.

The stems of the plant grow up to 30 or 40 cm long. Leaves are decussate, arranged oppositely in perpendicular pairs along the stems. The leaves are oval with thick, whitish, cartilaginous margins and measure up to 2 cm long. Flowers occur in leaf axils singly or in short, spikelike inflorescences. Each has four triangular sepals and four tiny pink petals.