Aloe
Aloe is a large genus of leaf-succulent plants in the family Asphodelaceae, native to Africa, Madagascar, the Arabian Peninsula and various Indian Ocean islands. The genus contains hundreds of species ranging from tiny, stemless miniatures a few centimetres across to tree-like giants several metres tall, and its members are prized by collectors for their sculptural rosettes of thick, often toothed leaves and their showy spikes of tubular flowers. The best-known member, the medicinal Aloe vera, is grown around the world, but the genus as a whole offers an enormous range of forms for the succulent enthusiast.
Description
Most Aloe species form a rosette of fleshy, water-storing leaves arranged around a short central stem. The leaves are typically thick and firm, lance-shaped or triangular in cross-section, and very often edged with teeth or soft prickles; many carry pale spots, banding, or a waxy bloom, and colours range from fresh green through blue-grey to bronze and deep red when stressed by sun and drought. Growth habits vary widely: some species stay solitary, others cluster into dense clumps by offsetting, and a number develop tall woody trunks or even branch into small trees.
The flowers are a defining feature of the genus. They are borne on erect, unbranched or candelabra-like spikes that rise well above the foliage, and are usually tubular and pendulous, in warm shades of red, orange, yellow, or occasionally near-white. Rich in nectar, they are pollinated by birds and insects in habitat and add a striking seasonal display in cultivation, often through the cooler months.
Aloe is sometimes confused with the New World genus Agave, but the two are unrelated: agaves generally flower only once and then die, whereas aloes flower repeatedly year after year and have softer, more gel-filled leaves.
Distribution
The genus is native to the Old World, centred on Africa. Its greatest diversity is found in southern and eastern Africa — particularly South Africa — with additional species in Madagascar, the Arabian Peninsula, and islands of the Indian Ocean such as Socotra. Aloes occupy a wide range of habitats, from coastal scrub and grassland to rocky slopes, cliff faces, and semi-desert, and this ecological breadth is reflected in the very different growth forms seen across the genus.
Because of their popularity, several aloes are now naturalised well outside their native range, and the genus as a whole is listed under CITES — most species on Appendix II and a number of threatened species on Appendix I — with the notable exception of Aloe vera, which is excluded from the appendices. Nursery-grown plants are widely available and legal to own and trade; wild collection is restricted.
Notable species
- Aloe vera — the familiar medicinal aloe, forming clumps of upright, gel-filled leaves; the most widely cultivated species in the world.
- Aloe arborescens — the "krantz aloe", a large branching shrub with orange-red winter flower spikes, popular as a hedge in mild climates.
- Aloe ferox — the "bitter aloe" or "cape aloe", a tall single-stemmed species with a crown of broad, spiny leaves.
- Aloe polyphylla — the "spiral aloe", famous for its striking spiral arrangement of leaves in five ranks; notoriously difficult in cultivation.
- Aloe aristata — a small, hardy, clustering rosette often grown as a beginner's houseplant (sometimes placed in the related genus Aristaloe).
- Aloe maculata — the "soap aloe", a variable, spotted, clumping species tolerant of a wide range of conditions.
- Aloe plicatilis — the "fan aloe", a slow tree-like species with leaves held in flat, distinctive fans (now often placed in the related genus Kumara).
Cultivation
As a group, aloes are among the more forgiving succulents, which is a large part of their appeal. They want bright light — full sun for most species, with a little shade for the more delicate miniatures and for plants acclimatising after winter — and a very free-draining, mostly mineral potting mix. Water thoroughly during the growing season once the soil has dried, then allow it to dry again; reduce watering sharply in winter, as cold combined with wet soil is the most common cause of rot. See Watering and Repotting for general technique.
Most aloes are tender and need protection from hard frost, though a handful of high-altitude and grassland species tolerate light freezes. Good air movement and unhurried watering will keep plants firm and well-coloured; many develop attractive red or bronze tones when grown hard in strong light. Overfeeding and overwatering, by contrast, produce soft, floppy, over-green growth prone to disease.
Propagation
Clustering species are easily increased by removing rooted offsets ("pups") from around the base of an established plant. Single-stemmed and shrubby aloes can be grown from stem cuttings, allowed to callus before potting. Species and new hybrids are also raised from seed, which germinates readily when fresh but readily hybridises, so seed-grown plants of garden origin are not always true to name.
Hybrids and cultivars
Aloes hybridise very freely, both between species and with related genera such as Gasteria and Haworthia, and this has given rise to a huge range of garden hybrids and named cultivars. Breeders have selected especially for compact rosettes, bold leaf spotting and texture, and richly coloured foliage, producing many small, colourful "designer" aloes ideal for pots and windowsills. Intergeneric hybrids are given hybrid genus names — for example ×Gasteraloe (Aloe × Gasteria) — and combine the toughness of aloes with the markings and patterning of their partner genus.
See also
- Aloe vera · Aloe arborescens · Aloe polyphylla — representative species
- Gasteria · Haworthia — related genera in the Asphodelaceae
- Soil and potting mix · Watering · Propagation - offsets · Propagation - seed · Repotting · Pests and diseases