Aquifoliales

Aquifoliales, holly order of flowering plants, containing more than 536 species in five families, mainly Aquifoliaceae. Aquifoliales belongs to the core asterid clade (organisms with a single common ancestor), or sympetalous lineage of flowering plants, in the euasterid II group of the Angiosperm Phylogeny Group III (APG III) botanical classification system (see angiosperm).

Aquifoliaceae

Aquifoliaceae, the holly family, contains the holly genus Ilex, with more than 400 species. Ilex is nearly worldwide in distribution, but it is best represented in mountainous areas of the tropics, especially in Asia, Central America, and South America. However, several well-known hollies range northward into southern Europe and the eastern United States. Ilex aquifolium (European holly) grows to 15 metres (50 feet) and furnishes valuable wood for veneers. It is used for decoration, and hundreds of horticultural varieties are available for ornamental plantings. I. opaca (American holly) is widely distributed in the warmer areas of the eastern United States, and it is grown in commercial orchards for its foliage and colourful berrylike fruits. Wood of this species is valuable in cabinetmaking and interior finishing. I. opaca is also an accent tree with more than 1,000 horticultural varieties and is used for street plantings and wind barriers and is even grown as bonsai. The dried leaves of I. paraguariensis are widely used in parts of South America to prepare a caffeine-rich beverage known as yerba maté.

Aquifoliaceae are shrubs or trees with alternate, sometimes toothed leaves that may have small glands on the lower surface of the blade. Some species are deciduous, but most are evergreen. The flowers are usually unisexual and occur on separate male and female plants. Thus, male and female hollies are planted close together in orchards to facilitate pollination. The sepals, petals, stamens, and carpels each number four to six parts or, rarely, more. The petals are generally slightly joined at the base, where the stamens are usually attached in a position alternate with the petals. The female flowers have a distinctive large stigma that sits directly atop the ovary (there is typically no style), and each chamber of the ovary generally has a single ovule on an axile placentation. Although hollies are usually pollinated by bees, their flowers lack nectary disks; sometimes the petals themselves produce nectar through swellings on their upper surface. The flowers are usually clustered into a cyme or umbel but may also be single in the leaf axils. The fruits of hollies are fleshy and are often brightly coloured when ripe. Technically, they are not berries but drupes, which have a stony pit embedded in the pulpy outer layer. When the fruit is dispersed, the embryo is often minute and barely developed; for this reason it may take up to a few years for germination to occur.

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Other families

Two small families in the order are closely related to Aquifoliaceae. Helwingiaceae, with the genus Helwingia, consists of three species of shrubs from eastern Asia. Phyllonomaceae has a single woody genus, Phyllonoma, with four species that range from Mexico to Bolivia. Both families have flowers in clusters that emerge directly from the leaf surface rather than from the stems. The flowers also feature inferior ovaries, well-developed nectaries, anthers free from the petals, and recurved stigmas. Helwingia has unisexual flowers and lacks sepals, whereas Phyllonoma has bisexual flowers with both petals and sepals.

Two closely related families are included within Aquifoliales. Stemonuraceae comprises 12 genera and 95 species found in tropical regions from Southeast Asia to Australia. The two largest genera are Gomphandra (55 species) and Stemonurus (15 species). The family is characterized by woody plants that have entire leaves with no stipules, small flowers in cymes, stout, hairy stamen filaments, and a broad, sessile stigma. Cardiopteridaceae includes five genera and about 45 species. The largest genus is Citronella, which has 21 species and was formerly included in Icacinaceae. This genus is unrelated to the citronella used as an ingredient in some insect repellents.