Agave sisalana (sisal hemp).

Abstract

Abstract Tropical succulent perennial of 1.5-2 m height, with thick leaves in a basal rosette of elongated sword-shaped leaves from the base. Stems: Two to three years after transplanting, a 20 cm tall stem is formed, which will reach a height of about 1.2 m when flowering. White, fleshy stems develop from underground buds at the base of the plant, first growing sideways and then upwards to form new plants. These new plants are known as suckers (DAFF, 2015). Trunk: The plant base is a short trunk (30-150 cm), from the top of which the spirally arranged leaves grow (DAFF, 2015). The components of the dry weight of sisal fibre are approximately 55-65% α-cellulose, 11-18% hemicelluloses, 7-15% lignin, 1% pectin and 1-8% ash (Elzebroek and Wind, 2008). Leaves: Stiff, heavy, persistent leaves that are 0.6-1.2 m long, 10.2-20.3 cm wide, and 2.5-10.2 cm thick when mature. Leaves are spirally arranged around the trunk, greyish-green in colour and covered by a layer of wax. Leaves contain coarse, cream-coloured or pale-yellow fibres (3%) (DAFF, 2015). Young leaves may have small spines along their margins; they disappear when the plant matures. Leaves have a terminal, dark brown, rigid, very sharp spine, 2-3 cm long. The cross-section at the base of the leaf resembles a flattened triangle (Elzebroek and Wind, 2008). Inflorescences: A large panicle with flowers arranged on the terminal portion in dense clusters, sessile, 4-5 cm long. Perianths with 6 segments, 6 stamens, filaments longer than the perianth segment, 3-4 cm long anthers. Style exserted, stigma 3-lobed (EOL, 2018). It only flowers once at around 2 years. Before flowering, a flower stalk of 4.5-6.0 m develops from the growth point. The flower stalk subdivides to form branches that bear the flowers. The flowers do not produce seed, but form bulbils, which are used for reproduction. Bulbils are borne in the axils of the bracteoles of the inflorescence after flowering. Flowers are yellowish green, with reddish filaments. Roots: A. sisalana has a shallow, fibrous root system up to 60 cm deep. The 2-4 mm thick root arises from leaf scars at the base of the bole beneath the soil surface, and extends up to 5 m horizontally way from the mother plant, forming suckers. These can be used for propagation (DAFF, 2015). Sisal produces subterraneous rhizomes from buds in the axils of the lower leaves. Along the rhizomes there are buds that may grow into new plants, forming colonies. Most of the roots are concentrated in the upper 40 cm of the soil, where they spread horizontally up to 5 m. A number of roots grow deeper than 40 cm, which results in good anchorage (Elzebroek and Wind, 2008). Fruit: This species is monocarpic (i.e., dies after fruiting). Fruits are capsules up to 6 cm long, 2-2.5 cm diameter, stipitate and beaked. Capsules rarely formed, and seeds (if any) are probably not viable. Vegetative bulbils are commonly produced below the flowers in the axils of bracts (Weber, 2003; Acevedo-Rodriguez and Strong, 2005).