Hymenachne amplexicaulis: A Review of the Literature
and Summary of Work in Florida

by
Kevin U. Hill

Introduction

        Hymenachne amplexicaulis (Rudge) Nees, is a robust, rhizomatous perennial grass, spreading on moist soil or floating in water. About eight species of the genus Hymenachne are generally distributed in the tropics of both hemispheres. It occurs throughout the West Indies, and tropical South and Central America in swampy situations on riverbanks and seasonally flooded land. This species is synonymized in Taiwan under H. pseudointerupta, (Li et al., 1978) and H. myurus (Howard, 1979). It was first characterized by Rudge in 1805 as Panicum amplexicaulis.

        Hymenachne was observed in Southwest Florida as early as the late 1970's at Owl Hammock near Immokalee by Mr. R.A. Roberts of Red Cattle Company. It has since been observed and documented by the author and others throughout many of the wetter areas of Collier County as well as in several other counties in South Florida including Lee, Charlotte, Hendry, Glades, Sarasota, and Desoto. How long this species has occurred in Florida, and the route of introduction is unknown, however, the relative proximity of known native habitats of hymenachne (e.g., Cuba, Dominican Rep., Jamaica) leaves open the possibility of natural introduction via migratory birds.

Morphology

        Hymenachne is commonly from 1 to 2.5m tall, erect, or ascending from a prostrate base, creeping or floating on water. Culms are filled with a white pith, often trailing and stoloniferous at the base and rooting at the nodes. Stems are glabrous, and leaves are lanceolate, cordate and clasping at the base, 20 to 35 cm long, and 2 to 3 cm wide. The ligule is membranous. Panicles are dense, spikelike, about 8 mm thick and 20 to 50 cm long, pedicels serrate.

Agronomic characters

        Hymenachne can form extensive colonies in its natural habitats. The better stands in Collier County occur in situations that tend to retain moisture for extended periods. This includes ponds with predominantly mucky soils, ditches, canal banks, and sandy depressional areas with a thick confining layer. This observation tends to agree with Medina and Motta, (1990) who demonstrated a relatively low drought tolerance for hymenachne. Hymenachne is well adapted to relatively deep levels of inundation, and will tolerate deeper water than will para grass (Brachiaria mutica) (Wildin, 1988). Tejos, (1980) reported that hymenachne withstood 40 weeks of flooding as well as a maximum flooding level of 121.5 cm. Wildin (1988) observed that hymenachne does not grow in permanent water, requiring alternating periods of flooding and dryness to establish and survive. These flooding and drying cycles allow massive regeneration by seed, thus ensuring persistence after extensive drought periods.

        In Florida, hymenachne flowers and sporadically sets viable seed during short days commencing in November which coincides with the end of the wet season. Germination has been variable, ranging from 86 to 0%. Factors affecting hymenachne seed fertility are not clearly understood.

        Hymenachne is sought after as natural grazing by cattle and wildlife throughout much of the year. Palatability remains high even at advanced stages of growth after flood waters have receded (Bogdan, 1977). Jiminez and Escobar (1977) reported that hymenachne was found to make up the highest portion (34.96%) of the diets of cattle grazing seasonally flooded savannas in Venezuela. Protein content was also highest (10.44 ± 1.82%) among grasses grazed in a study area consisting of bank, transitional, and waterlogged zones.

        Dirvin (1962), conducted a study in Surinam in which the forage quality of hymenachne was examined. Crude protein content was found to be high with 15.8% in the whole plant, the leaves containing 22.6% CP, and the stems, 8.9% CP. Crude protein digestibility was also found to be high (66-80%) and it was higher in the stems than in the leaves.

        In a study by Tejos (1980), at Apure, Venezuela, forage productivity of hymenachne was examined. Annual forage DM production during the flooding period was an average of 4.2 t/ac and ranged from a high of 8.1 t/ac to a low of 2.6 t/ac. During the dry season, average production was 3.1 t/ac. It was also shown that during the flooding period, hymenachne exhibited a slightly higher dry matter content in the leaves than in the stems, while the opposite held true during the dry period. Dirvin et al., (1960) also reported wide ranging annual DM yields for hymenachne grown in Surinam rice field fallows with values ranging from 1.7 to 9.19 t/ac.

Field Studies in Florida

        Initial investigation of hymenachne in Collier County by the author was limited to the gathering of plant samples for quality analysis. This involved harvesting available forage of plants under grazing at selected sites on the Immokalee Ranch, commencing in April 1989. Samples included both leaf and stem tissue as was typically grazed by the cattle. Results indicated that CP content was high, (12.6 to 30.3%) with TDN values ranging from 54.2 to 75.9%.

        A yield study was initiated in May 1990 at two ponded locations on the Immokalee Ranch in Collier County. Grazing exclosures (16' x 20') were constructed at each location in naturally established stands of hymenachne growing on Chobee muck soil. Four treatments were established with 4 replications in a randomized complete block design: 30, 60, and 90 day regrowth, and an unclipped control. Each plot was harvested to a 3" stubble height. No treatment received any lime or fertilizer.

        Forage harvests were scheduled on a calendar basis (30 days). Dry matter yield was determined on samples oven dried at 60øC. Crude protein content and total digestible nutrients (TDN) were determined via wet chemistry by the Div. of Chemistry Feed Laboratory, Florida Dept. of Agriculture and Consumer Services, Tallahassee.

        Shortly after establishing the study, one location became heavily infested with dog fennels as a result of the extremely dry spring. It was decided to continue the study for 1990 using only the Tippen's Crossing location.

Results to Date and Discussion

        Results indicated average CP content to be high regardless of cutting interval (Table 1.). Values observed were 15.0, 14.4, and 12.2% for 30, 60, and 90 day regrowth periods respectively. TDN values ranged from 50.1 to 52.7%.

Table 1. Total DM yield and quality of Hymenachne amplexicaulis harvested
at three cutting intervals from May to September.
Treatment - Cutting Interval
30 days 60 days 90 days
CP, %* 15.0 14.4 12.2
TDN, %* 52.7 51.9 50.1
DM, %* 6.66 5.93 2.71
*Values expressed as a percent of the dry matter.

        Yield data indicated that a 30 day cutting interval resulted in the highest average DM yields (6.66 t/ac), but by the end of the study (4 cuttings) some decrease in stand vigor was observed. There was no detectable reduction in plant vigor for those plots harvested at 60 day intervals. These results suggest that hymenachne will support heavy repeated grazing, but will require periodic rest periods during the growing season.

        Some flowering occurred in the 90 day and control plots as early as August, but 30 and 60 day treatments, as well as the surrounding grazed area delayed flowering until the end of October.

        The study was concluded prematurely after the October harvest, since high water levels prevented access to the plots.

Incidence in Collier County

        With cooperation from the Collier County office of the USDA Soil Conservation Service, areas of current incidence or potential development of hymenachne were mapped using a GIS system. Databases used included the USDA-SCS soil survey, and the Florida Game and Freshwater Fish Commission Land Use Code Classifications.

        It was determined by visual observation that hymenachne occurs predominantly on Chobee muck soils that are included in SCS soil classification series 22 and 43. These soil series were cross referenced with vegetative plant communities of freshwater marshes, wet prairies, and cypress swamps to determine areas of potential for hymenachne. Figure 2 shows all areas in Collier County where hymenachne has been documented and figure 3 displays areas where potential for development exists.

Summary

        It is recognized that actual acreage of land in Collier County suitable for establishment of hymenachne is limited. However, hymenachne does produce considerable tonnage of high quality forage which tends to retain its palatability and a relatively high level of quality well into late Fall. This suggests that hymenachne may serve as an effective "protein-bank" grazing source for a Fall/Winter range grazing program in some areas of South Florida.

        Additional work is needed to determine areas and limits of adaptation in Florida, means of establishment, methods of management, and factors affecting seed production. Also, while it is apparent that hymenachne has been a part of the Florida range landscape for many years, careful study and monitoring for invasive potential should be conducted.

Literature Cited:

Bogdan, A. V. 1977. Tropical Pasture and Fodder Plants (Grasses and Legumes). Longmans: London. pp. 152-153.

Dirvin, J. G. P. 1962. De voederwaarde van bladeren en stengels bij tropische grassen. Surin. Landb. No. 5, pp.199-202.

Dirvin, J. G. P., I. G. H. Dulder, and W. C. Hermelijn. 1960. De braakvegetative op risjstvelden in Nickerie. Surin. Landb. 8. No. 1, pp.1-7.

Hitchcock, A. S. 1936. Manual of the Grasses of the West Indies. United States Department of Agriculture, Miscellaneous Publication 243. p. 312.

Howard, R. A. 1979. Flora of the Lesser Antilles Leeward and Windward Islands. Vol 3, Arnold Arboretum, Harvard University.

Jiminez, E. G., and A. Escobar. 1977. Flood Adaptations and Productivity of Savanna Grasses. Proceedings of the 13th International Grasslands Congress. Section 3-4-5.

Li, Hui-Lin. 1978. Flora of Taiwan. Vol. 5. Epoch: Taiwan.

Medina, E., and N. Motta. 1990. Metabolism and distribution of grasses in tropical flooded savannas in Venezuela. J. of Trop. Ecology. 6:77.

Roberts, R. A. 1989 Personal communication. Immokalee, Florida.

Tejos, M. R. 1980. Production of water straw grass (Hymenachne amplexicaulis (Rudge) Nees) during a savanna period. Congreso Venezolano de Zootecnia, Guanare (Venezuela) p. 54.

Wildin, J. H. 1988. Register of Australian Herbage Plant Cultivars. Tropical Grasslands Journal. 22.4:190.

Wildin, J. H., and D. G. Chapman. 1987. Ponded pasture systems - capitalising on available water. Queensland Dept. of Primary Industry Bulletin RQR 87006.

Last modified: Saturday, May 04, 1996 9:36:37 PM
Kevin U. Hill, Extension Livestock Agent, Collier County, kuh@gnv.ifas.ufl.edu