Monochoria hastata
(hastate-leaved pondweed)

Monochoria hastata is a tropical aquatic herb, almost entirely restricted to its native distribution of South-East Asia and Oceania (Boonkerd et al., 1993). It is a weed of rice fields in South-East Asia, with a prolific seed production and a high capacity to reproduce vegetatively (Ali et al., 2018). It is only listed as invasive in rice fields in Singapore, without further details (PIER, 2019). M. hastata is not reported as invasive in natural habitats; nor is there information about its effects on biodiversity.

Outside its native range, M. hastata is reported as expected to spread and invade rice fields in Pakistan, facilitated by flooding events associated to monsoon rains (Ali et al., 2018). Although is not found in the New World, M. hastata is declared as a Federal Noxious Weed in the USA, because of the detrimental effects it could cause to agriculture (Coile, 1996).

In Oceania, M. hastata is reported only as cultivated in Fiji, without further details (PIER, 2019). In the Northern Territory of Australia, M. hastata is classified as vulnerable because of the deterioration of aquatic habitats and the invasion of exotic weeds (India Biodiversity Portal, 2019).

M. hastata is a tropical perennial herb native to South-East Asia and Oceania (Steenis, 1947; Boonkerd et al., 1993). Outside of its native range, the species has been reported from Pakistan (Ali et al., 2018) and Fiji (Greenwood, 1949; PIER, 2019). It is regarded as possibly not native to Singapore because it is found only in artificial water bodies (The DNA of Singapore, 2019). Although it is reported in Brazil (India Biodiversity Portal, 2019), according to Flora do Brasil (2019) it is not present in that country. For details, see the Distribution Table (Ali et al., 2018; Flora of China, 2019; India Biodiversity Portal, 2019; PIER, 2019; The DNA of Singapore, 2019).

M. hastata is an aquatic herb with a medium to high risk of introduction into tropical areas worldwide. It is apparently confined to tropical areas, and it is not spreading into subtropical or temperate regions. Boonkerd et al. (1993) reports it as being unable to survive winter temperatures in subtropical areas.

M. hastata could be introduced to suitable areas through its use as an ornamental, flooding events and interconnected waterways (Ali et al., 2018; Useful Tropical Plants, 2019). Because of its presence as a weed of rice and the possible detrimental effects on agriculture, M. hastata is listed as a noxious weed in the USA (USDA-NRCS, 2019). Although it has not been reported as a contaminant of rice products, its spread through cultivation practices needs more research.

M. hastata is a tropical aquatic herb reported from freshwater pools, mudflats in rivers, ditches, rice fields, canal banks, sluggish streams, silted-up meanders, swamps, open drains and very wet soils (Reiner and Robbins, 1964; Boonkerd et al., 1993; Kosaka et al., 2013; India Biodiversity Portal, 2019; PIER, 2019; The DNA of Singapore, 2019; Useful Tropical Plants, 2019). It grows from sea level to 700 m altitude (PIER, 2019).

M. hastata is reported as a weed of rice fields, but with very little information available (PIER, 2019). Boonkerd et al. (1993) report that at high population densities, M. hastata is competitive and can reduce rice yields considerably.

Genetics

The chromosome numbers reported for M. hastata are n=17, 40, 42 (Eckenwalder and Barrett, 1986). There are no germplasm collections or breeding programmes reported for the species (Boonkerd et al., 1993).

Patwary et al. (1989) collected four distinct morphological types of M. hastata and M. vaginalis; two from each species. According to the authors, M. vaginalis type II is an allotetraploid derived from the M. hastata type I × M. vaginalis type I and that M. hastata type II is an autoallohexaploid hybrid of M. vaginalis type II × M. hastata type I.

Reproductive Biology

M. hastata reproduction is by seeds and vegetatively by rhizome fragmentation (Boonkerd et al., 1993; Useful Tropical Plants, 2019). Anthesis takes place during the morning and the flowers are self-compatible (Boonkerd et al., 1993; Huelsenbeck et al., 2003). In India the flowers are foraged for pollen by Apis mellifera (Pal and Karmakar, 2013). The seeds are produced in abundance and the germination is underwater (Ali et al., 2018). For cultivation, the seeds should be sown as soon as they are mature (Useful Tropical Plants, 2019).

Physiology and Phenology

M. hastata is a fast-growing perennial aquatic herb that can grow either rooted in wet soil or floating in water (Boonkerd et al., 1993; Ali et al., 2018). The Inflorescences and leaf blades are always borne above the water level. It is reported as flowering from March to August in India (India Biodiversity Portal, 2019).

Longevity

M. hastata is a perennial aquatic herb (Boonkerd et al., 1993). It is also reported as an annual by Hakim et al. (2013), but this probably refers to the plants dying if fields dry out (Boonkerd et al., 1993).

Population Size and Structure

Plants of M. hastata usually grow in clumps (India Biodiversity Portal, 2019).

Associations

Vibrio cholera-O1 has been found in the roots of M. hastata in Bangladesh (Islam et al., 1994). Endophytic fungi of the genera Curvularia, Trichoderma, Penicillium and Fusarium are reported from the leaves of M. hastata by Chowdhury et al. (2016).

Environmental Requirements

M. hastata is a tropical aquatic herb growing best in sunny areas with temperatures of 25- 35°C, tolerating 16-38°C. It prefers an annual rainfall of 1500-2000 mm, tolerating 1000-4000 mm. It can grow in very wet soils and in water, becoming a floating plant in deeper water. It prefers fertile, medium to heavy soils with a pH range of 5 to 6.5, tolerating pH 4 to 7 (Useful Tropical Plants, 2019).

The insects Hippotion echeclus and Rhopalosiphum nymphaeae have been reported as herbivores of M. hastata (Encyclopedia of Life, 2019).

Animal feed, fodder, forage

• Fodder/animal feed

Environmental

• Amenity

General

• Sociocultural value

Human food and beverage

• Vegetable

Medicinal, pharmaceutical

• Traditional/folklore

Ornamental

• garden plant

Monochoria hastata is similar to M. vaginalis (Ali et al., 2018; PIER, 2019). The rhizome in M. vaginalis is short while in M. hastata it is longer and branched. The leaves of M. hastata usually have a sagittate or hastate base whereas in M. vaginalis they are obtuse, rounded or truncate-cordate. M. hastata usually has more flowers per raceme than M. vaginalis. The flowers of M. hastata do not open simultaneously and the pedicels are unequal in length, being longer at the base of the raceme.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Warning Systems

M. hastata is included in the USA Federal Noxious Weed List, with the importation of plant parts, seeds or products being prohibited (Coile, 1996; USDA-NRCS, 2019).

Chemical Control

Although no specific information is available, the use of herbicides in rice fields reduces the incidence of weeds in general (Boonkerd et al., 1993).

Research is required on the impact of M. hastata on rice fields, and also on natural habitats and biodiversity.

31/10/19 Original text by:

Jeanine Vélez-Gavilán, University of Puerto Rico at Mayagüez, Puerto Rico