Macrotyloma axillare (PROSEA)
Macrotyloma axillare (E. Meyer) Verdc.
- Protologue: Kew Bulletin 24: 402 (1970).
- Family: Leguminosae
- Chromosome number: 2n= 20
Dolichos axillaris E. Meyer (1836).
- Axillaris, perennial horse gram (En).
Origin and geographic distribution
Axillaris originates in sub-Saharan Africa, from Ethiopia to Senegal and south to the Transvaal and Natal in South Africa (16°N to 31°S latitude). Var. axillare extends to Madagascar and Arabia, and var. glabrum (E. Meyer) Verdc. to Madagascar, Mauritius and Sri Lanka, but var. macranthum (Brenan) Verdc. is more restricted and is only found from Tanzania to Zimbabwe. Cultivar "Archer" has become naturalized in small areas of eastern Australia and Papua New Guinea.
Axillaris is used as a perennial sown pasture legume in Australia where it is grazed during the growing season or used as stand-over feed early in the dry season.
In Australia N concentrations of whole tops of "Archer" fell from 2% in the early wet season to 1% in the dry season. Phosphorus concentrations, on a high-P soil, fell from 0.25-0.30% (early wet season) down to 0.12-0.17% (dry season). Seed contains about 4% N and 0.45% P.
The plant is not toxic, but has a bitter taste which may cause stock to reject it until they get used to it. It sometimes taints the meat of lambs when fed as a large part of their diet for a long time, and so could taint milk in similar circumstances. Across a range of accessions, there were 50-200 seeds/g (80-90 in "Archer").
Perennial climbing or trailing twining herb with a strong woody taproot and rootstock. Stems do not root at the nodes; stems cylindrical, glabrescent or hairy, > 5 m long if climbing, otherwise usually < 3.5 m; the main axis is strongly ascending on young plants. Leaves trifoliolate; leaflets entire, elliptical, ovate-lanceolate, ovate or subrhombic, 1.1-7.5 cm × 0.7-4.2 cm, rounded to acuminate and mucronulate at the apex, rounded to subacute at the base, glabrous to pubescent, somewhat glossy above and paler beneath; stipules ovate-lanceolate, 2-5 mm long, veined. Flowers axillary in 2-4(-10)-flowered clusters; peduncles very short or absent; standard oblong-elliptical, 1-2.4 cm × 0.6-1.5 cm, whitish or greenish-yellow with a crimson or purplish spot inside near the centre; stigma surrounded by a ring of short dense hairs. Pod shortly stipitate, linear-oblong, 3-8 cm × (5-)6-8 mm, glabrous or pubescent, containing (5-)7-8(-9) seeds. Seed rounded or ellipsoid, compressed, 3-4.2 mm × 2.5-3 mm × 0.6-1.5 mm, smooth and hard, buff to dark red with sparse to very dense black mottling.
Growth and development
Flowering is delayed in the year of sowing, but not subsequently, which is indicative of a juvenile phase during which flowering is inhibited. This also seems to apply to the regrowth of individual shoots on mature plants. Flowers are cleistogamous but honey bees can transfer pollen between them once they are open. Pods usually mature 4-8 weeks after flowering and shatter readily once dry.
Other botanical information
Three varieties are recognized; var. axillare and var. glabrum have flowers 1.2-1.5(-2) cm long; those of var. macranthum are larger, (1.5-)2-2.4 cm long. The first two varieties may be distinguished by stem indument: var. axillare has dense, spreading hairs and var. glabrum has sparse, adpressed hairs although intermediate types are fairly common. "Archer", which is the only cultivar, released in Queensland, Australia, is close to var. glabrum .
Axillaris is essentially a tropical or subtropical short-day plant from grassland, woodland, forest margins and coastal dunes. It is common in disturbed places such as fallow land and roadsides in its natural range. It prefers relatively mild conditions (optimum day/night temperature for growth is about 26/21 °C) so is better adapted to low altitudes in the subtropics and higher altitudes, up to 2250 m, in the tropics. Although top growth is killed by frost, it regrows from the rootstock in spring in the subtropics. It is drought-hardy but not very productive if rainfall is less than 800 mm/year. It grows best on well-drained soils such as alluvial sandy loams and basaltic clay loams, and it is moderately shade-tolerant. It is not well adapted to heavy clays, or infertile, acid (pH(H2O) < 5.5) solodic soils, and it will not tolerate waterlogging or saline soils.
Natural ecotypes have been collected under a range of conditions: rainfall 700-1400 mm/year; growing season 140-365 days; mean maximum temperature of the hottest month of the growing season 26-31 °C; mean minimum of the coldest month of the growing season 11-24 °C; and mean minimum of the coldest month of the dry season 3-18 °C.
Propagation and planting
Hand harvested and threshed seed may be very hard and require scarification. Mechanically harvested or threshed seed is usually satisfactory for sowing without further treatment to break hard-seededness.
In prepared seed-beds, seed may be drilled 1-2.5 cm deep and lightly covered, or else broadcast and harrowed. Axillaris can also be established in natural woodland by broadcasting seed mixed with fertilizer into the ashes after burning at the beginning of the wet season. Recommended sowing rates are 2-4 kg/ha in pure stands and 0.5-1 kg/ha in mixtures. Inoculation is not usually necessary, but the rhizobium strain CB 1024, or its equivalent, should be used if inoculation is required. Early growth is rather slow. Axillaris combines well with a wide range of grasses and is often sown in mixtures with other twining or scrambling legumes.
Axillaris competes very well with weeds once established and has been deliberately used to control shrubby weeds by allowing the axillaris to grow without grazing from winter into spring in Australia. Axillaris will usually overtop weedy grasses by early autumn in the year of sowing.
"Archer" will not grow well on soils poor in P or S without fertilizer. Compared with centro ( Centrosema pubescens Benth.), it has a higher requirement for K, but similar requirements for Cu.
Diseases and pests
There are no serious disease or pest problems with axillaris. Individual plants may be stunted and killed by the mycoplasma "legume little leaf", but the productivity of the sward is scarcely affected. It is susceptible to root-knot nematodes ( Meloidogyne spp.) but control measures are unpractical.
Axillaris is harvested by grazing animals rather than by cutting, although hay making is possible provided care is taken to conserve leaf. Its major strength lies in providing better stand-over feed in the early part of the dry season and faster growth in the early part of the wet season than most other tropical legumes which shed their leaves more readily and only grow slowly in the early wet season. Thus it is often sown on ridges above the frost line. Rotational grazing is best, and swards should not be grazed lower than 15 cm because axillaris will not withstand frequent close grazing.
In Australia, axillaris has yielded 16 t/ha of DM under irrigation and 3-4 t/ha without irrigation. In India, green yield of an axillaris/green panic ( Panicum maximum Jacq. var. trichoglume Robijns mixture (39 t/ha) exceeded that of the grass alone (24 t/ha). DM yields of fertilized swards under regular cutting at three sites in the highlands (1200-1500 m) of northern Thailand ranged between 1.5-7.6 t/ha in the second year.
Seed yields of 100-150 kg/ha are common. Yields of more than 550 kg/ha are possible from small areas, especially if the sward is harvested just before the pods start to shatter and is then allowed to dry. Large-scale seed crops are difficult to handle with normal heading equipment because the pods are borne closely intermixed with the long tough stems and shatter as soon as they are dry.
The present world collection of axillaris is held at ATFGRC (CSIRO, Australia) and CIAT (Colombia). It contains a fair representation of material from Kenya to South Africa, but the remainder of the natural range is poorly represented.
There are no known breeding programmes. Its main limitations of pod shattering, which increases the cost of seed production, lack of long-term persistence under continuous heavy grazing and limited adaptation to relatively mild climates could possibly be overcome by further collection from other parts of the natural range or by gene transfer from related species (e.g. indehiscent pods from M. uniflorum (Lamk) Verdc.).
The main strengths of axillaris are its drought and disease resistance, its vigorous growth in summer, and the valuable grazing it provides in early winter and early spring in the subtropics. However, unless its climatic adaptation can be broadened and its resistance to heavy grazing improved, then it is only likely to play a minor, though locally very useful, role. It is showing promise in Bolivia, Brazil, China (Hainan Island), Ghana, Guatamala, India, Panama, the Philippines, and Thailand, and could play a useful role in upland areas in most tropical countries.
- Blumenthal, M.J., O'Rourke, P.K., Hilder, T.B. & Williams, R.J., 1989. Classification of the Australian collection of the legume Macrotyloma. Australian Journal of Agricultural Research 40: 591-604.
- Cameron, D.G., 1986. Tropical and subtropical pasture legumes. 10. Axillaris (Macrotyloma axillare): a legume with limited roles. Queensland Agricultural Journal 112: 59-63.
- Gillett, J.B., Polhill, R.M. & Verdcourt, B., 1971. Macrotyloma. In: Milne-Redhead, E. & Polhill, R.M. (Editors): Flora of tropical East Africa. Leguminosae 4 - Papilionoideae 2. Crown Agents for Oversea Governments and Administrations, London. pp. 581-594.
- Luck, P.E., 1965. Dolichos axillaris - prospects in Queensland. CSIRO Australia, Division of Plant Industry, Plant Introduction Review 1(3): 50a-51a.
- Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 177-178.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 346-349.