Asparagales

Asparagales is the name of an order of plants, used in modern classification systems such as the APG III system (which is used throughout this article). The order takes its name from the family Asparagaceae and is placed in the monocots. The order has only recently been recognized in classification systems. It was first put forward by Huber in 1977 and later taken up in the Dahlgren system of 1985. Before this, many of its families were assigned to the old order Liliales: a very large order containing almost all monocots with colourful tepals and without starch in their endosperm. DNA sequence analysis indicated that Liliales should be divided into at least Liliales, Asparagales and Dioscoreales. The boundaries of the Asparagales and of its families have undergone a series of changes in recent years; future research may lead to further changes and ultimately greater stability.

The order is clearly circumscribed on the basis of DNA sequence analysis, but is difficult to define morphologically, since its members are structurally diverse. Thus although most species in the order are herbaceous, some no more than 15 cm high, there are a number of climbers (e.g. some species of Asparagus), as well as several genera forming trees (e.g. Agave, Cordyline, Yucca, Dracaena), some of which can exceed 10 m in height. Succulent genera occur in several families (e.g. Aloe).

One of the defining characteristics of the order is the presence of phytomelan, a black pigment present in the seed coat, creating a dark crust. Phytomelan is found in most families of the Asparagales (although not in Orchidaceae, thought to be a sister to the rest of the group).

Almost all species have a tight cluster of leaves (a rosette), either at the base of the plant or at the end of a more-or-less woody stem; the leaves are less often produced along the stem. The flowers are in the main not particularly distinctive, being of a general 'lily type', with six tepals, either free or fused from the base.

The order is thought to have first diverged from other related monocots some 120-130 million years ago (early in the Cretaceous period), although given the difficulty in classifying the families involved, estimates are likely to be uncertain.

From an economic point of view, the order Asparagales is second in importance within the monocots to the order Poales (which includes grasses and cereals). Species are used as food and flavourings (e.g. onion, garlic, leek, asparagus, vanilla), as cut flowers (e.g. freesia, gladiolus, iris, orchids), and as garden ornamentals (e.g. day lilies, lily of the valley, Agapanthus).