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Persea is a genus of 200–240 species of small to large evergreen trees, found mostly in eastern Asia and Central and South America, with a few species in eastern North America and one on eastern Atlantic islands (Macaronesia). They are usually single-stemmed, with a rather smooth, pale brown bark; younger stems and branches often remain green and smooth for many years, eventually becoming corky. Leaves are alternate, borne at the tips of the branches, simple in shape with entire margins, and are usually rather firm in texture; in many species the young leaves flush bronze, brown or red. The inflorescence consists of several subterminal, axillary panicles, the individual flowers small and inconspicuous, borne on short pedicels that may become fleshy and enlarged in fruit. The flowers are bisexual, with six perianth segments in two whorls arising from a short tube, the perianth segments persisting and sometimes enlarging, but not becoming appressed to the fruit; stamens six to nine, in two to three whorls; stigma and ovary solitary. The fruit is a berry, usually small and black, sometimes much larger, green or purplish.
Generic limits within the Lauraceae are often difficult to define, but there seems to be wide acceptance now of Kostermans’ (1974) inclusion in Persea of Asian species formerly placed in the genus Machilus – species with reflexed persistent perianths at fruiting (in Persea s.s. the perianth segments are either deciduous or persist in appressed or patent positions when in fruit) – although the name Machilus is still regularly found in horticultural literature. Specific delimitation seems to be somewhat easier, with the species described here all being recognisably distinct. Persea is famous for the large fruits of the Avocado P. americana but most species have rather small fruits that are adapted for dispersal by birds, and the familiar avocados – dispersed principally by primates but much loved also by carnivores (Jaguars in the Americas, Leopards in Africa) – are in fact unusual in the genus.
The Lauraceae contribute to horticulture some of the finest of broadleaved evergreens, and Persea is firmly established in the pantheon of the very elite, with bold glossy green foliage often preceded by a striking spring flush of red, brown or glaucous leaves. In general its members are much less well known than they ought to be, especially in Europe – perhaps because they do enjoy a hot summer, but maybe also because they seem too improbably exotic to be thought worthy of a trial. The long-term success of the Chinese P. ichangensis in southern England indicates that this is not necessarily true. The yellowish inflorescences of Persea, while composed of the usual small lauraceous flowers, are comparatively conspicuous and may form an attractive feature as growth starts in spring; they can also be pleasingly fragrant.
The hardier species should be planted in a warm site, preferably with some shelter from cold winds and late frost, especially when young. An acid to neutral soil seems to be most suitable, and ample moisture during the summer is an important requirement. Avocados are susceptible to Phytophthora root rots, especially P. cinnamomi, and these may also cause trouble in the temperate species. Propagation is by seed or by grafting onto suitable rootstocks; cuttings are most successful when taken in late summer and rooted with heat and mist (Hogan 2008).
A genus of evergreen trees mainly confined to tropical and warm temperate regions, but extending as far north as Japan, S. Korea, and central China. Leaves alternate, pinnately veined. Flowers bisexual, in axillary inflorescences. Perianth segments six; stamens twelve in four rows, the innermost set reduced to staminodes. Pistil one, with a single style. Fruit a fleshy berry, usually with the perianth-segments persistent at the base, one-seeded. The species treated below is, so far as is known, the only one truly hardy in the open air in the British Isles. It was originally described in Machilus, but this genus has been included in Persea by Kostermans (Reinwardtia, Vol. 6, pp. 189-94). P. borbonia (L.) Spreng. of the south-eastern USA, and P. lingue Nees of Chile, could probably be grown outdoors in the mildest parts. The latter is a valuable but rare timber tree, with very handsome fruits.
The best known species of Persea is P. americana Mill. (P. gratissima Gaertn. f.), the fruit of which is the avocado of commerce. Cultivated in the warmer parts of the New World since pre-Columbian times, its distribution as a wild tree is not known for certain, but it is probably native from southern Mexico to northern South America. It is now grown as an orchard tree in many of the warmer parts of the world, including the Mediterranean region. There are many named varieties, propagated by budding, which differ in the size of their fruits, in the texture of the skin, which varies from leathery and smooth to shell-like and warted; and in their season of fruiting. The common name derives from the Mexican 'ahuacatl' through the Spanish 'aguacate'.
The genus Machilus was included in Persea by Kostermans in Reinwardtia, Vol. 6, pp. 189-94(1962).