September 21
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Plant Genus of the family Rutaceae

Genus Description Cultivation
Agathosma These 135 heather-like shrubs and subshrubs belong to the family of Rutaceae, and are native to the southwestern Cape in South Africa. There is some commercial cultivation for buchu oil (a diuretic), which is also used in artificial blackcurrant flavorings and various herbal treatments. Most of these plants are 15?24 in (38?60 cm) tall and slightly less in spread. The plant is densely covered with small narrow leaves, often rolled at the edges. The small 5-petalled flowers are in axillary clusters or umbels, ranging from white through to red-mauve and occasionally yellow. The whole plant is aromatic. CULTIVATION: These plants should be grown in neutral to acid, humus-rich sandy soil with added grit in full sun. In areas that get frost in winter they are better grown in containers. They can then be grown outdoors in summer, ready to be taken in as the weather gets colder. They need moderate watering during the growing season and feeding with a balanced fertilizer once a month. Watering should be reduced as the weather becomes colder. The plants need to overwinter in frost-free conditions, even if some species can survive short spells of 32?F (0?C). Propagation is from seed in spring, in lime-free compost with added grit, or from ripe cuttings in summer.
Agonis This is a relatively small genus consisting of 12 evergreen species all found growing naturally in the temperate regions of the southwest of Western Australia. The most widely grown, Agonis flexuosa, is the only tree among this group of shrubs, however it is the lower-growing cultivars of this species which are more popular for garden use. The name Agonis is from the Greek, agonis, meaning ?without angles?, and refers to the weeping branch habit of some species. All have white or pink flowers resembling those of the tea-tree (Leptospermum) to which they are related. In common with other members of the myrtle family, the leaves contain aromatic oil which is released when the leaves are crushed. The fibrous bark, although not of particular interest to gardeners, is a distinguishing feature of the genus. CULTIVATION: This is an adaptable, almost pest-free genus, suited to a full sun position in a wide range of well-drained soils and climates, although some species can be damaged by frost. While tip pruning can be done at any time to encourage bushier growth, the trees will also respond to pruning after flowering. Propagate by seed or cuttings, but remember that cultivars will only come true if cuttings are taken.
Backhousia This genus consists of 7 evergreen species of both shrubs and trees, all of which occur in the subtropical and tropical rainforests of the east coast of Australia. All the members of this genus have a neat attractive habit with white or cream-colored flowers which have prominent stamens and aromatic mid-green foliage. One species, Backhousia citriodora, the lemon-scented myrtle, is now being cultivated commercially for culinary purposes. CULTIVATION: This genus of rainforest plants does best in rich, well-composted soil, which ensures sufficient moisture is retained to be freely available at all times. Although partial shade is appreciated while young, plants often flower more profusely in full sun. Propagation is by cuttings or by fresh seed.
Boronia Noted for sweet fragrance, early spring blooms and aromatic foliage, this genus belongs to the citrus family, Rutaceae, and consists of around 100 species, the majority occurring in Australia. Ranging in size from small to medium-sized, compact, evergreen shrubs, they have simple or pinnate leaves, and the small 4-petalled flowers may be open and star-shaped or bell-like with overlapping petals. Flower colors range from white, pink, bluish mauve, red, yellow, yellow-green and brown. Some species are short lived and success is often achieved when grown in containers that can be easily moved to protected or shady positions in hot or windy weather. CULTIVATION: Locate boronias in sheltered positions with the protection of other plants in sun or part-shade. The soil should be well drained with a fairly high organic content so that it does not dry out readily during hot or windy weather. If growing in pots ensure that the potting mix does not contain added fertilizers with high phosphorus levels. The flowers generally last well when picked and the plants benefit from the trimming. After flowering, up to one half of the plant can be removed to prolong life and improve bushiness. Propagation is from half-hardened tip cuttings.
Citrus Ranging in the wild from China to India, Southeast Asia, New Guinea and Australia, this genus comprises about 20 species of evergreen shrubs and small trees. Some species and many hybrid cultivars are grown in warmer countries of the world for their edible fruits, the oranges, lemons, limes, grapefruit and mandarins among others. Recent studies have concluded that all the major citrus fruits have evolved in cultivation from just 3 wild parent species, namely the citron (Citrus medica), the shaddock or pomelo (C. maxima) and the mandarin (C. reticulata). Oranges, lemons and grapefruit are hybrids between these 3 wild species. And botanists have also concluded that the cumquats, hitherto separated into the genus Fortunella, do not differ in any essential way from Citrus and must therefore be included in it. The same goes for the Australasian species hitherto included in Microcitrus and Eremocitrus. Highly ornamental, the citrus family crops longer than any other fruit tree and their dark glossy foliage holds its attractive appearance throughout the year. The fragrant, white, star-shaped flowers appear singly or in clusters at different times of the year, depending on the variety. The fruit structure is unique and is what identifies the genus. The tough skin, dotted with numerous tiny oil-filled cavities, encloses a white ?pith? of greatly varying thickness, within which the characteristic segments are contained. Each segment is packed with juice-filled vesicles which develop from hairs lining the walls of the flower?s ovary, each hair consisting of a single cell. CULTIVATION: In frost-free conditions most citrus thrive in fertile well-drained soil in a sunny position protected from wind. During the growing season they need plenty of water and regular small applications of nitrogenous fertilizer to promote growth and fruit size. In general, citrus need very little pruning, except to remove shoots arising from below the graft union and, when mature, to remove dead or damaged branches and overcrowding within the tree. Citrus grown on dwarfing rootstocks make excellent decorative and productive fruiting trees for large pots. These should be positioned where they receive plenty of sunlight and shelter from wind; where frosts are common they should be moved under cover over winter. Propagation is by budding or grafting the desired citrus onto a suitable rootstock.
Dictamnus
Phellodendron This is a genus of 10 species of deciduous trees from temperate East Asia that, somewhat surprisingly, falls within the citrus family. Notable for their aromatic foliage and corky bark, they have large pinnate leaves composed of broad, often glossy leaflets. While their flowers are small and yellow-green in color, they are carried in panicles that are often large enough to be conspicuous, though not very showy, and are followed by small, black, fleshy fruits. The autumn foliage, however, is often bright yellow and can be spectacular in some years. CULTIVATION: Most species in this genus need a climate with distinct seasons, and a cool winter is important to ensure proper dormancy. On the other hand, they also handle with ease hot summers and harsh sun, though the foliage is easily damaged by strong winds. They seem to thrive in any well-drained soil with a position in full sun. Plants may be propagated from seed, cuttings, by layering or grafting.
Poncirus The single species in this genus within the family of Rutaceae is a deciduous shrub or small tree native to China and Korea, where it grows in open woodland. Related to citrus, it will cross with those and is often used as a hardy rootstock for oranges and other citrus cultivars. It is grown for its interesting winter form showing deep green branches with stout thorns. It is a dense fast-growing shrub suitable for hedging. CULTIVATION: It does best in full sun, despite growing in woodland in the wild. It needs fertile and free-draining soil and protection from cold drying winds. Propagate by sowing seed in a position protected from frost in autumn or taking half-hardened cuttings in summer.
Ptelea Despite looking rather more like lilacs than oranges, and bearing sycamore-like seeds, the 11 deciduous shrubs or small trees in this North American genus are citrus relatives. This is only apparent in the aromatic oil glands of the foliage, which is usually trifoliate, with a dominant central leaflet flanked by a smaller one on each side. The leaves often become bright yellow in autumn. The small white to pale green flowers are scented and clustered together in conspicuous cymes. They appear first in spring or early summer, then sporadically afterwards. Small, 2-seeded, winged fruit, a little like hop seeds, follow. CULTIVATION: Species from southern USA and northern Mexico are a little tender. Otherwise, most are adaptable and easily grown in any well-drained soil in sun or partial shade. In areas with hot summers, some shade from the afternoon sun is advisable. Propagate from seed, layers or grafts.
Ruta Mostly subshrubs, some of the 8 species that make up this genus can become shrubby in mild climates. The genus, found throughout temperate Eurasia, is renowned as the source of several herbs that since ancient times have been used both medicinally and in beverage manufacture. The foliage is a grayish blue-green and finely divided. Small yellow flowers in cymose heads appear in summer and are followed by insignificant greenish seed heads. CULTIVATION: These plants are very easily grown in any well-drained soil, preferably in full sun. Established plants may be trimmed to shape, but hard pruning is seldom necessary. Propagate from seed or half-hardened cuttings.
Zanthoxylum This is a widespread genus of around 250 species of deciduous or evergreen spiny shrubs and trees with pinnate leaves and aromatic bark from North and South America, Africa, Asia and Australia. They are grown for their attractive habit and handsome aromatic foliage, and sometimes for their fruits that are dried and used for spices. Some species have medicinal properties and others provide a fine timber used for cabinet-work. CULTIVATION: Depending on the species, they are frost hardy to frost tender. They need a fertile, moist but well-drained soil with a position in full sun or partial shade. Pruning is rarely necessary, but young specimens may be shaped in early spring. Propagate from seed, cuttings and rooted suckers.



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