Water Amaranth (Figure 39).

Figure 39 Water amaranth scientific name Ammannia baccifera Linn. ear-leaved water amaranth (Figure 40).

Figure 40 Earleaf water amaranth scientific name Ammannia arenaria H.B.K. Multiflora water amaranth (Figure 41).

Figure 41 Multiflora water amaranth Scientific name Ammannia multiflora Rox b. Family Classification Chitinaceae, Water amaranth. Morphological features water amaranth 10-50 cm tall; stem erect, four-angled, much branched, lilac, with narrow wings. Leaves are opposite, sometimes slightly alternate on upper or lateral branches. Leaf blade lanceolate, oblanceolate or long elliptic, larger on the stem, sometimes up to 5 cm long, 1.2 cm wide, smaller on lateral branches, 0.6-3 cm long, 0.2-0.6 cm wide, apex acute or obtuse, base cuneate, tapering into a short stipe, lateral veins inconspicuous. Flowers several in axillary cymes, usually crowded. The common pedicel is short, ca. 0.1 cm or nearly absent, the pedicel 0.1-0.2 cm long, the flowers very small, 0.1-0.2 cm long, purplish red. Bracts linear-subulate, calyx tube campanulate, 4-toothed, lobes triangular, 2-3 times shorter than calyx tube, hemispherical when fruiting, enclosing lower half of capsule, usually without petals; stamens usually 4, adnate to middle of calyx tube, as long as or slightly shorter than calyx lobes. Ovary globose, style very short or absent. Capsule globose, purplish red, ca. 0.1-0.2 cm in diam. and irregularly dehiscent above middle. Seeds very small, subtriangular, black. Ear-leaved water amaranth is distinguished from water amaranth by sessile, linear-lanceolate or narrowly lanceolate leaves, 1.5 to 5 centimeters long, 0.3 to 0.5 centimeters wide, with a cordate auriculate base. Flowers axillary, arranged in laxer cymes, usually 3 to 7-flowered, the common pedicel fine, 0.3 to 0.5 cm long. Bracts and bracteoles 2. linear. Petals 4, yellowish or white, ca. 0.1 to 0.2 cm, caducous. Stamens 4 to 6, style longer than or equal to ovary. Multiflora water amaranth is distinguished from ear-leaved water amaranth by the following: the bases of the leaves on the lower part of the stem are cuneate, the cymes are denser; the flowers are smaller, usually more than 15, the common pedicel is very short, about 0.1 to 0.2 centimeters, with petals, and the style is shorter than the ovary, about 0.1 centimeters, and the diameter of the capsule is about 0.1 to 0.2 centimeters.

Biological characteristics 1) dormancy and germination seeds with dormant period, although the winter has been lifted, but water amaranth is an aquatic weed, seed germination requires high water, in the soil water supersaturation or thin water when germination is better, less germination in the state of humidity, drought conditions do not germinate, and therefore the period of occurrence of the late. Because the seed is small, can only shallow germination, germination of the starting temperature of 16 ℃, but low temperature when the germination is slower, the average temperature of 20 ℃ above the germination of the better, the occurrence of a long period of time, rice throughout the entire reproductive period can occur. 2) Nutritional growth water amaranth in shallow water growth is better, the growth of the wet state of growth is worse, in the long term under the conditions of wetness, the plant grows short, not branched, water amaranth shade resistance, do not tolerate bright light irradiation, like to live It likes to be born in paddy fields. But still require more adequate light, in the rice before sealing rows of water amaranth growth is better, rice growth in the middle and late occurrence of water amaranth, due to too much shade, the growth of the weaker, shorter. Ear-leaf water amaranth, multi-flower water amaranth and rice relative height can reach more than 0.8. 3) Flowering and fruiting water amaranth belongs to the short sunshine plant, rice field, flowering period in August to October, fruiting period in September to October, in the rice in the middle and late stage of the occurrence of water amaranth, shade in rice rows can still be able to bloom and fruiting, but the amount of fruiting is less.

Distribution and damage water amaranth, ear leaf water amaranth, multi-flowering water amaranth is mainly distributed in the Yangtze River Basin and its south, the Yellow River Basin, Hebei, Shaanxi, Gansu also have distribution, often three kinds of water amaranth mixed in the rice field, in the irrigation conditions are better, the field is often shallow water in the rice paddy occurs more, and often with the knapweed, strangler, etc. constitutes the group, become an important weed in the late stage of rice growth.