Stylosanthes hamata (L.) Taub.

Leguminosae

Synonyms

Hedysarum hamatum L.; Stylosanthes procumbens Sw.; S. eriocarpa Blake.

Caribbean stylo (Australia); pencil flower, mother segal (West Indies); tebeneque (Venezuela).

A herbaceous annual to short-lived perennial with a non-determinate, much-branched, semi-erect growth habit. It can reach 0.75 m. Stems spreading to ascending, with a dichotomously branching habit, smooth, except for a very fine line of white hairs down one side, but no bristles. Leaves trifoliate with long, narrow, shiny leaflets, the latter 4.5 to 5.3 times as long as they are wide. Stipules 4 to 6 mm long, bidentate, adnate to the base of the petiole, hairs on the sheath and teeth. Inflorescence an oblong spike, greater than 20 mm long, with 8 to 14 small yellow flowers on a long stem. Outer bracts have hairs on the edges, one outer and two inner bracts and an axis rudiment subtending each flower. Loments have two articulations, both usually fertile, the lower pilose, the upper glabrous. Beak slightly curled, equal to or shorter than the upper articulation, total length of upper pod including beak 6 to 7 mm, a few hairs on the underside of beak. Seeds medium to dark brown, 2 to 2.5 mm long, unsymmetrically reniform, radicle ends fairly prominent (McKay, personal communication).

S. hamata occurs mainly in the West Indies, in the Caribbean area generally, and in coastal areas of Venezuela and Colombia bordering the Caribbean. It also occurs in coastal areas of southern Florida, United States. It is occasionally reported from Honduras and various parts of Brazil but these may not be native populations, especially those growing in isolated areas in southern Brazil.

A summer-growing plant. Cv. Verano flowers in 65 to 75 days after planting, thus approximating the early- to mid-season-flowering types of Townsville stylo. However, unlike Townsville stylo, vegetative growth and flowering can continue throughout the rest of the season.

Aerial growth is cut even by light frosts but the crowns will survive moderate frosts.

S. hamata is essentially a low-altitude, maritime plant, lacking the cold tolerance necessary for growth at higher elevations.

600 to 1700 mm per year, with 700 to 900 mm ideal. S. hamata requires a pronounced dry season for optimum growth.

'Verano' is certainly more drought tolerant than Townsville stylo and is sufficiently drought hardy to survive the long dry season in the dry tropics of northern Australia. To ensure persistence of the crown, however, considerable leaf fall may occur.

Certain forms have quite good flood tolerance (Brohlman, 1978).

Soil requirements are fairly specific for each ecotype . 'Verano' is suited to the infertile, acid, sandy-surfaced solodics that suit Townsville stylo but with some tolerance of slightly more alkaline soils, such as the duplex texture-contrast brigalow (Acacia harpophylla)/dawson gum (Eucalyptus cambageana) soils of central Queensland. Other forms, in Florida and Antigua, have thrived on alkaline soils varying from coarse coral beach sands to relatively heavy clays (Burt et al., 1983).

'Verano' is promiscuous, nodulating freely with a wide spectrum of native cowpea rhizobia in Australian soils. Other ecotypes are much more specific and lack of suitable Rhizobium strains has held back the testing of some lines.

The rhizobially promiscuous 'Verano' spreads readily and widely, the hooked upper seed pod being spread readily by stock. The more specific types may be slower in spread, depending on how quickly appropriate rhizobia can travel.

Requirements are similar in most respects to those of Townsville stylo. The better the seed bed and the more complete the removal of competing plants, the more successful will be the establishment. However, both strip planting and oversowing into burnt native pasture have been quite successful in northern Australia.

Because only half the seed pods carry a beak and the hook is not as long and complete as-that of Townsville stylo, S. hamata seed tends to flow more freely than that of Townsville stylo. As a result, an even wider range of-sowing methods can be used. Most seed is distributed either from the air or by ground spreading from fertilizer spinners, in the latter case mixed with a small quantity of fertilizer as a carrier.

Surface sowing is possible, but shallow coverage of the seed enhances establishment success, especially on soils with a tight-setting surface.

In the seasonally dry tropics, where break of the seasonal drought is reliable, the ideal sowing time is just before the beginning of the next wet season. In northern Queensland, this is from December to early January. Sowing rates of 1 to 4 kg. of seed/ha are used.

Cv. Verano has about 270 000 seeds in the pod and 450 000 without pods.

For 'Verano', hard-seed levels are high immediately after seed set. Seed softens more slowly than that of Townsville stylo, though high surface soil temperatures hasten softening (McKeon and Mott, 1984).
When planted on bare burnt surfaces, commercial seed will soften quickly if planted some weeks before the break-of-season rains. However, if planted into a moist conventional seed bed, such as is used for seed production, seed should be scarified before sowing. In some circumstances, half of the seed is treated and half left hard. The hard seed softens naturally and gives an insurance against a false start to the first growing season. Scarification can be by dry heat (Mott, 1979), hot water or dehulling.

Like all Stylosanthes spp., Caribbean stylo has the ability to forage strongly for phosphorus in the soil. As a result it can grow on quite low phosphate soils. It will nevertheless respond strongly to applied phosphate, establishment in particular being aided by a small quantity of superphosphate. Cv. Verano responded to applied P in the same degree as Townsville, Cook and endeavour stylo (Jones, 1974).
Responses have also been widespread to molybdenum and sulphur applications. Plants in calcareous soils apparently have much higher phosphorus requirements for adequate growth.

Cv. Verano is no more tolerant of shading by strong grass growth than is Townsville stylo, but, because of its rather more vigorous growth, it can keep up above the grass for longer. As a result, it combines well with Urochloa mosambicensis and Bothriochloa pertusa, two grasses planted or often naturalized in areas where 'Verano' is planted in north Queensland.

Like all the Stylosanthes spp., 'Verano' appears remarkably tolerant of a wide range of herbicides. For seed production, Trifluralin (40 percent w/v) at 1.4 to 2.0 litres/ha is recommended preplant, followed by 2,4-D amine (50 percent w/v) at 1 litre/ha of the product after the plants are 5 cm high and 2 litres/ha of product on established crops. Alachlor, dinoseb, paraquat, dimethaline and aciflourfen all seem to be effective herbicides for use in seed crops, but actual recommendations are not yet available (English and Hopkinson, 1984).

As with Townsville stylo, management, through adjustment of stocking rate, should aim at suppression of the associated grass should this show signs of dominating the stand, especially early in the growing season. Heavy grazing is readily tolerated and reduces the competition from taller-growing grasses while the stylos form a dense, ground-hugging mat of foliage. Perennation of individual plants could also be favoured by close grazing, inasmuch as plants left ungrazed throughout their growing season tend to behave as annuals.

'Verano' has no tolerance of dry-season fire, perenniating plants being readily killed. However, hard seed is softened by the fire and the stand is generally replaced at the beginning of the next growing season.

Like Townsville stylo, S. hamata makes excellent hay so long as it is cut before leaf fall commences. If left too late, it can give a rather stemmy hay.

Unlike Townsville stylo, 'Verano' continues vegetative growth after flowering begins, and will continue to grow while seasonal conditions remain suitable. This gives a longer season of nutritious feed in some years, but once the soil dries out, leaf fall can be rapid and standover feed of little value, consisting mainly of bare stems.

Protein levels are reasonable and in vitro digestibilities are in the order of 60 to 65 percent. The phosphate levels of the forage however depend on the status of the soil in which the stylo is growing. On low phosphate soils, low levels of forage phosphorus can be expected, especially toward maturity.

None recorded.

Direct heading is the usual method with 'Verano' in north Queensland, but suction harvesting can sometimes be used under very intensive management conditions. For direct heading, correct timing is essential. Flowering should have ceased or nearly so, and some seed should already have been shed. Most seeds should be no longer green but brown (English and Hopkinson, 1984).

Yields of up to 700 kg./ha have been obtained for seed in the pod in north Queensland for 'Verano' . Normal commercial yields are in the range of 300 to 600 kg./ha.

'Verano' is currently the only commercial cultivar. Released in Australia in 1973, it was collected in 1965 at Maracaibo Airport, Venezuela (10°N lat., elevation 10 m, MAR 563 mm), but it is believed that other cultivars of diploid types are under development in Florida and the West Indies. 'Verano' could in fact be a separate species (Stace and Cameron, 1984).

To date, 'Verano', while showing some susceptibility to anthracnose (Colletotrichum gloeosporioides) in the greenhouse, has remained, for all practical purposes, resistant or at least tolerant to the ravage of anthracnose in the field. It is also susceptible to botrytis head blight (Botrytis cinerea) in high-rainfall areas and to rhizoctonia web blight (Rhizoctonia sp.), but these cause little damage in the main 'Verano' areas, which are located in drier districts.

Essentially a bigger, better, short-lived perennial form of Townsville stylo with, to date, anthracnose tolerance and a better competitive ability with native grasses in northern Australia.

'Verano' is very much a tropical plant, performing poorly at higher latitudes and especially in the subtropics.

'Verano' has replaced Townsville stylo with the latter's collapse to anthracnose. Its greater competitive ability, drought resistance and wide soil adaptation were already giving promise of its being a complementary species to Townsville stylo before the appearance of anthracnose.

McKeague, Miller and Anning (1978); Burt et al. (1983); English and Hopkinson (1984).

S. hamata grows between 12 and 28° latitude. It is doubtful that the plant is native to areas outside these limits (Williams et al., 1984).

Caribbean stylo competes better with weeds than does Townsville stylo, because of its more vigorous growth and weak perenniality.

'Verano', at least, is a heat-loving plant, and in Queensland, Australia, does not perform well south of the Tropic of Capricorn.

'Verano' is essentially a self-pollinating, cleistogamous plant, pollination occurring within the flower before it opens. There is, however, a low level of cross-pollination that can occur even with related species such as S. scabra. Unlike most S. hamata ecotypes, which are only diploids with 2n = 20 chromosomes, 'Verano' is a tetraploid line with 2n = 40.

Provided the native grass growth is not strong and the impeding cover is removed by burning, quite successful establishment is possible. Where stronger competition exists, light cultivation will be desirable.

The Queensland standard is 40 percent minimum germination plus a maximum of 20 percent hard seed deemed to be germinable. Minimum pure seed content is 90 percent.