Desmanthus pubescens


Scientific name

Desmanthus pubescens B.L. Turner

Turner (1950) regarded Desmanthus virgatus as an all-encompassing species, comprising D. virgatus , D. pubescens , D. pernambucanus , D. glandulosus and D. leptophyllus .  Despite taxonomic revision by Luckow (1993) that resolved the complex to distinct species, many authors continued to refer to all species as D. virgatus in the literature until the late 1990s.  Correct nomenclature is now generally used.

Synonyms

    

Family/tribe

Family: Fabaceae (alt. Leguminosae) subfamily: Mimosoideae tribe: Mimoseae.  Also placed in: Mimosaceae.

Common names

guashillo, chinchibe, alta missa (Mexico).

Morphological description

Erect woody shrub to 1.5 m tall, strongly branching from the base.  Young stems green and hairless, angular with golden corky ridges.  Older stems hairless, shiny red or brown, with a waxy, shedding cuticle.
Compound bipinnate leaf 2.5-5.7 cm long with 3-7 pairs of pinnae 10-30 mm long and 11-22 pairs of leaflets/pinnae, 2.2-5.0 mm long and 0.7-1.1 mm wide.  Petiole 4-10 mm long.  Persistent stipules 2.5-7.0 mm long.
Small flowering heads (condensed spikes) 0.7-1.0 cm long, occur singly in leaf axils on short peduncles (1.0-4.5 cm long).  Heads contain 8-13 flowers that may be perfect, functionally male or sterile.  Sterile flowers occur rarely, when present 2-4 occur at the base of the head.  Male flowers occur towards the base of the head above the sterile flowers, but below the perfect flowers and number 0-4.  Perfect flowers (4-8 in number) occur apically and are 2.0-3.0 mm long.  Fruiting stalks 1.5-4.2 cm long bear 2-11 pods.
Pods are linear or recurved, 4.5-8.5 cm long and 3.2-3.9 mm wide, opening along both margins.  Reddish-brown to nearly black at maturity.
Seeds 13-22/pod, 2.4-3.2 x 1.9-2.4 mm, flattened and ovate in shape and reddish-brown or black in colour.

Distribution

Native to:
Occurs in dense stands in marshy coastal areas through Mexico, Belize, and Guatemala at altitudes of 0-200 m.  Also occurs on rocky clays and sands in Cuba.

Uses/applications

A component of a blend of three Desmanthus spp. released as cv. Jaribu for use in permanent pastures on heavy soils in subtropical and tropical Australia.  Has potential for use in long-term (>3 years) phase pastures in cropping systems, although establishment difficulties because of small seeds is a limitation.  Shrubby desmanthus is also used as a hedgerow species in alley cropping systems with forage or crop species planted seasonally, or as a protein bank for animal feed in India, and D. pubescens could be used in this way.

Ecology

Soil requirements

Occurs on a range of soil types from sandy and gravely soils to calcareous soils and rocky clays.  In exotic locations, Desmanthus spp. are generally selected for their persistence on heavy clays, including alkaline soils, but will grow productively on lighter soils of neutral to alkaline reaction.

Moisture

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In its native range, D. pubescens occurs in dense stands in swampy areas, but also in drier areas along roadsides in environments receiving an average annual rainfall of 1,000-1,800 mm, with a moderate 4-6 month dry season. 
Well-adapted to 550-1,000 mm average rainfall environments in exotic locations and will tolerate extended dry periods.

Temperature

Native to lowland tropics where average annual temperatures range from 23-27°C and with only minor monthly fluctuations in temperature .  It is reasonably cold tolerant, growing into the subtropics in exotic locations.  Although defoliated by heavy frosts, it will regrow from crowns once there is sufficient heat and moisture.

Light

Poor tolerance of medium to heavy shade.

Reproductive development

In the native range (16°N-21°N), flowers from December to April and fruits from February to June.

Defoliation

Tolerant of regular cutting and grazing by ruminants.  One of the forage legumes most tolerant of heavy grazing in pastures on clay soils in sub-humid, northern Australia.

Fire

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Will regrow from the crown after moderate fire.

Agronomy

Establishment

As with all small seeded legumes, establishment on clay soils is unreliable.  For most successful establishment sow scarified seed no deeper than 2.0–2.5 cm into moist soil, and preferably into a cultivated seedbed with good subsoil moisture.  D. pubescens has larger seed than D. virgatus and will tolerate slightly deeper planting depths.  Surface broadcasting onto a well-prepared seedbed, followed by rolling has given good results.  It has also been successfully planted into cultivated strips in established grass pastures, or sod-seeded into slashed pasture treated with glyphosate to suppress grass growth.
Fresh seed is extremely hard-seeded and should be scarified, either abrasively (eg. using a rice polisher) or by hot water treatment (4–10 seconds in boiling water), to raise the germination to a minimum of 50–70%.  It is important to achieve good establishment from the plant crop, as seed produced from paddock plants will remain hard-seeded for 2–3 years.
In Australia, desmanthus has previously been sown as cv. Jabiru, a mix of D. virgatus (cv. Marc), D. leptophyllus (cv. Bayamo) and D. pubescens (cv. Uman).

Fertiliser

May respond to S, Mo, P, Cu and Mn on clay soils.  A critical leaf tissue concentration of 0.2% S is required for optimum productivity.  Highest DM yields at a P-deficient site were achieved with the addition of 50 kg/ha at Maharashtra, India, and 80 kg/ha P2O5 at Texas, USA.  Higher rates of P-fertiliser decreased DM yields at both sites.

Compatibility (with other species)

Its deep-rooted habit enables it to be grown with stoloniferous and other competitive grasses.  D. pubescens has formed productive mixtures in exotic, sown pastures as well as with useful native species.  In northern Australia, plant crops of cv. Uman generally persist strongly in buffel grass (Cenchrus ciliaris ) and other tropical grass pastures, but long term persistence is commonly poor due to low seed production in the late-flowering cv. Uman and the extreme hardseededness of any seed that is produced.   Note that all accessions of D. pubescens studied are late flowering. Controlled grazing during flowering and seed development may improve persistence.

Companion species

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Grasses:  Cenchrus ciliaris , Panicum coloratum var. makarikariense, Dichanthium sericeum .

Pests and diseases

Occasional, minor damage by psyllid insects (Accizia spp.) was reported in northern Australia.  The psyllids cause more serious damage in seed crops.  Several seed-eating bruchid beetles (5 Acanthoscelides spp. and 1 Stator sp.) are known to infest Desmanthus .  No other reports of serious pests and diseases were cited.

Ability to spread

Being very late flowering and producing only limited seed under grazing, spread of cv. Uman in central and southern Queensland has been limited and in many instances it has not persisted.  In northern (tropical) Queensland, cv. Uman produces abundant seed.

Weed potential

Has potential to become a weed of disturbed areas due to its high seed production and erect, woody habit , but is not currently listed as a major weed.

Feeding value

Nutritive value

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Evaluations generally do not distinguish between species of Desmanthus, and are based on cvs. Marc, Bayamo and Uman.  Crude protein content of the entire plant ranged from 10.5-15.5%, with leaves averaging 22.4% and stems 7.1%.  A study of 18 accessions grown in India reported an average CP content of 21% (range 15-27%), and average NDF and ADF contents were 42. and 35%, respectively.
In sacco DMD and N concentration of CPI 92803 were 70% and 2.3% respectively.

Palatability/acceptability

Moderately palatable to grazing ruminants.  Lower than for leucaena (Leucaena leucocephala ) but higher than Stylosanthes scabra cv. Seca.

Toxicity

No toxicities to ruminant livestock are reported in the literature.  Desmanthus spp. do not cause bloat in ruminants because they contain 2–3% (of total DM as tannic acid equivalent) condensed tannins.

Production potential

Dry matter

Generally more productive than D. virgatus but less productive than D. leptopyllus .

Animal production

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In a pen feeding experiment where a Mitchell grass (Astrebla spp.) basal diet was supplemented with cv. Uman, DM intake of Merino wethers increased from 580 to 720 g/head/day, and wool growth increased from 0.48 to 0.65 g/day/cm2.
No grazing trials assessing animal liveweight gains from D. pubescens are reported in the literature.

Genetics/breeding

Taxonomic confusion within the genus has led to a vast range of accessions from D. pernambucanus , D. leptophyllus , D. pubescens and D. virgatus being evaluated as D. virgatus .  Genetic and phenotypic diversity in D. pubescens is limited and this will restrict the development of new cultivars.  Level of out-crossing is low.  No breeding work has occurred with the species to date.

Seed production

Seed yields of 400-500 kg/ha are achieved from direct-headed crops, but considerable seed losses occur due to uneven ripening and early seed fall.  The potential seed yield using a suction harvester is in excess of 1,000 kg/ha, however the suction required to collect the dense Desmanthus seed can result in large quantities of small stones in the sample.
Late-flowering types require an extended period of favourable moisture conditions to flower and set seed.  A high proportion of under-developed, immature embryos that are non-viable or of low vigour can occur in late-flowering types grown in sub-tropical environments where frosting and moisture stress may occur during seed development.  These seeds are of similar dimensions to fully mature seeds and are therefore very difficult to remove during conventional seed grading.
A psyllid insect (Accizia spp.) can cause severe damage to seed crops in Australia and may need to be controlled using insecticides.
In Jhansi, India, seed production was increased by adding 60 kg/ha P2O5 .

Herbicide effects

Killed by Access® herbicide (120 g/L picloram and 240 g/L triclopyr).

Strengths

  • High rates of seed production in tropical frost-free regions.
  • Tolerant of heavy grazing.
  • Persistent in low rainfall environments.
  • Tolerant of alkaline, sodic, saline and heavy clay soils.
  • Has potential as a phase legume in cropping systems.

Limitations

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  • Can be difficult to establish on clay soils because of small seed size.
  • Poor regeneration from seed in sub-tropical environments.
  • Becomes stemmy when ungrazed or lightly grazed.
  • Highly specific in its Rhizobium requirements (CB3126).

Other comments

Recruitment from seed in grass-legume pastures will not occur until hardseededness has been overcome by weathering.  This will require several seasons to occur.

Selected references

Burt, R.L. (1993) Desmanthus: a tropical and subtropical forage legume . Part 1. General Review. Herbage Abstracts, 63, 401–413.
Gardiner C.P. and Burt R.L. (1995) Performance characteristics of Desmanthus virgatus in two contrasting tropical environments. Tropical Grasslands, 29, 183–187.
Hopkinson, J.M. and English, B.H. (2004) Germination and hardseededness in Desmanthus. Tropical Grasslands, 38, 1–16.
Jones, R.M., Bishop, H.G., Clem, R.L., Conway, M.J., Cook, B.G., Moore, K. and Pengelly, B.C. (2000) Measurements of nutritive value of a range of tropical legumes and their use in legume evaluation. Tropical Grasslands, 34, 78–90.
Jones, R.M. and Brandon, N.J. (1998) Persistence and productivity of eight accessions of Desmanthus virgatus under a range of grazing pressures in subtropical Queensland. Tropical Grasslands, 32, 145–152.
Luckow, M. (1993) Monograph of Desmanthus (Leguminosae-Mimosoideae). Systematic Botany Monographs, Vol. 38. The American Society of Plant Taxonomists.
Pengelly, B.C. and Liu, C.J. (2001) Genetic relationships and variation in the tropical mimosoid legume Desmanthus assessed by random amplified polymorphic DNA. Genetic Resources and Crop Evolution, 48, 91–99.
Spiers, P.R.., Brandon, N.J., Date, R.A., Bahnisch, L.M. and Gearge, D.  (1998) Nutrient limitations of clay soils for Desmanthus virgatus II. A glasshouse study of 7 soils. Tropical Grasslands, 32, 6–12.

Internet links

Cultivars

Cultivars

Country/date released

Details

'Uman'
(CPI 92803)
Australia A very late-flowering cultivar (about 135 days), growing to a height of 40–100 cm.  Best suited to the humid tropics.  Has persisted in trial plots in semi-arid 450 mm AAR areas of north-western Queensland on clay soils.

Promising accessions

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Promising accessions

Country

Details

CPI 92801, CPI 92802, CPI 92804, CPI 92807, CPI 92811, CPI 92812 and CPI 92813 Australia Similar to cv. Uman
The low level of genetic diversity in D. pubescens will limit development of new cultivars.