Hymenachne amplexicaulis | |
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Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Clade: | Monocots |
Clade: | Commelinids |
Order: | Poales |
Family: | Poaceae |
Subfamily: | Panicoideae |
Genus: | Hymenachne |
Species: | H. amplexicaulis |
Binomial name | |
Hymenachne amplexicaulis (Rudge) Nees | |
Hymenachne amplexicaulis, also known as West Indian marsh grass in the US, Olive hymenachne in Australia, and hereafter referred to as hymenachne, is New World species [1] in the genus Hymenachne . Hymenachne is from the Greek hymen meaning "membrane" and achne meaning "chaff, glume, scale" and amplexicaulis is from Latin, literally "embracing the stem" or "stem-clasping. [2] [3] This freshwater species is native to the tropical and subtropical regions of the West Indies, Northern South America, and Central America. [4]
Hymenachne is a perennial grass that primarily reproduces via stolons. [4] This robust species is commonly found growing 1–2.5m tall. [4] The stems are hairless and float prostrate across the top of the water, then grow upright from these bases to support leaves. [4] The flat, triangular leaves (10–45 cm long, up to 3 cm wide) have a prominent clasping bases, or auricles. [4] The auricles help to distinguish it from other invasive wetland grasses and the native H. acutigluma in Australia. [5] Hymenachne has been shown to increase the stem length between nodes to keep leaves above water during periods of flooding. [6] Its stem is packed with airy tissue called aerenchyma to help the stems float and to aid in flood tolerability. [5]
Hymenachne flowers in the early fall and seeds in late fall. [7] The flower is a panicle [8] that can grow to half a meter. [5] Researchers at the University of Florida have seen multiple panicles per plant originating from branching at a single node. [9] Hymenachne can produce thousands of seeds with up to 98% germination right off the panicle. [10] [11] [12]
Hymenachne prefers constantly inundated soil and is known to survive comfortably in about a meter of water for 20 years. [5] [13] This species was shown to survive poorly in Australia where flooding exceeded 1.2 m. [14] [12] In its native range in Venezuela, and in invaded areas of Florida, hymenachne was documented to survive in >1.2m of water for nearly a year. [15] [16] Hymenachne has also been found in water greater than 4m deep persisting in floating mats, likely dislodged after a storm event. Conversely, hymenachne is not recorded to survive sites that entirely desiccate. [17]
Hymenachne is known to colonize and form dense monocultures in floodplains, roadside ditches, and lake margins in invaded and native areas. [14] [18] [19] [4] It is often found colonizing areas with little shading and competition from other species. [5] Although limited information is available on soil preferences of hymenachne, it has been found in deep, poorly drained muck soils in Florida. [20] It is not found in waters with a significant salt concentration. [21] [5]
There have been three introductions of hymenachne into Australia, one in Florida, and one in Louisiana. [22] [23] [5] Australia now lists hymenachne as one of the top twenty worst weeds. [24] Hymenachne invasions have been shown to decrease species richness, increase invasive fish populations, and overall cause fundamental changes in floral and faunal composition in Australia. [13] Hymenachne was introduced in Australia as forage for cattle, and likely for the same reason in Florida. [5] The species was used in ponded pastures, or artificial ponds created to hold water for use in the dry season. [5] High reproducibility from stem fragments aids in the dispersal and invasion of this species. [10] The first herbarium record of hymenachne in Florida is from 1957. [23] [25] The second specimen is not recorded until 1977. [25] The cause for this gap is unknown; however, today it is recorded in 28 counties across the state. [26] [27]
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