Apiales: Morphology

The Apiales belong to the large group dicotyledons. There are a number of characteristics that are unique to this order. One of these characteristics, which is limited to the Apiales and a few members of the Sapindales and Cornales, is the petroselinic acid contained in the seeds in considerable amounts. Another characteristic is the multiplicity of locules, the chambers of the ovary containing seeds, each locule having a single ovule. Other characteristics that are more easily recognized are the compound or cleft leaves and the separate petals as opposed to fused petals. A compound leaf has two or more leaflets attached to a common axis such as the leaves on carrots or celery. On celery the stalk of the leaves is the part of the vegetable that we eat (Cronquist, 1988). The main kinds of flowers found on Apiales are simple or compound umbels. A single umbel has the many stalks of individual flowers arising from the same point on the flower stalk. These stalks of each flower grow so that they reach the same height giving the plant its characteristic flat-topped appearance. A compound umbel, as opposed to a single umbel, further contains several small umbels arranged into one larger umbel (Cronquist, 1988).

The family Apiaceae (Umbelliferae) is mainly temperate herbaceous plants and usually appears as creepers or tree like shrubs. Several members of this family also develop a spiny appearance. The leaves are typically alternate, although entire leaves can be found in species such as Bupleurum. The small and simple flowers are generally arranged into compound umbels. They have five petals that are usually colored white or yellow, five stamens, and an ovary with two carpels and two locules, one for each ovule. The fruit that develops from this ovary varies considerably within the family. Generally the fruits are schizocarps, dry fruits that contain two cambers, each developing into one seed. The two seeds of a schizocarp are separated by an artition and remain together until they reach maturity and then fall apart (Heywood, 1993).

The family Araliaceae mainly consists of tropical and temperate herbs, shrubs and trees. The best known members are ivy and ginseng. Many botanists have found it difficult to distinguish between the Apiaceae and the Araliaceae due to the many similarities in floral and vegetative features. Like the Apiaceae, the leaves of Araliaceae are alternate although often compound and larger. Many leaves of this family are also covered with hair. Another feature that the two families have in common is the arrangement of the flowers into umbels -- although in the case of Araliaceae the umbels are more often single than compound. As also is the case with Apiaceae, the ovary of Araliaceae has several locules each with a single ovule. Araliaceae, though, seldom has a fruit that is a schizocarp and instead contains an indeterminate number of seeds with plenty of endosperm (Heywood, 1993).

Araliaceae differs from Apiceae in a number of ways. The petals, for example, are sometimes five, as is the case with Apiaceae, but often only three in number. These petals are white or pale green in color. Another way in which Araliaceae differs is in having species that are equipped with aerial roots specially modified for clinging or support (Heywood, 1993).

Pittosporaceae are evergreen shrubs and small trees that live in the tropics. Unlike Apiaceae and Araliceae the leaves are usually entire, often evergreen and leathery. The flowers typically have five petals. The ovary is contained within two or five fused carpels and has one or many locules. The seeds that develop from the ovaries are covered with a brownish resin. The seeds are plentiful, have a copious endosperm and are dispersed in several different ways. Sometimes they have wings in order to be dispersed by wind. Other times the fruits are capsules or drupes, fleshy fruits with a hard pit, dispersed by birds or other animals (Heywood, 1993).