Order (Plantae): Asparagales

Asparagales (asparagoid lilies) is an order of plants in modern classification systems such as the Angiosperm Phylogeny Group (APG) and the Angiosperm Phylogeny Web. The order takes its name from the type family Asparagaceae and is placed in the monocots amongst the lilioid 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 and then the APG in 1998, 2003 and 2009. Before this, many of its families were assigned to the old order Liliales, a very large order containing almost all monocots with colorful tepals and lacking starch in their endosperm. DNA sequence analysis indicated that many of the taxa previously included in Liliales should actually be redistributed over three orders, 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. In the APG circumscription, Asparagales is the largest order of monocots with 14 families, 1,122 genera, and about 36,000 species.

The order is clearly circumscribed on the basis of molecular phylogenetics, but it is difficult to define morphologically since its members are structurally diverse. Most species of Asparagales are herbaceous perennials, although some are climbers and some are tree-like. The order also contains many geophytes (bulbs, corms, and various kinds of tuber). According to telomere sequence, at least two evolutionary switch-points happened within the order. The basal sequence is formed by TTTAGGG like in the majority of higher plants. Basal motif was changed to vertebrate-like TTAGGG and finally, the most divergent motif CTCGGTTATGGG appears in Allium. One of the defining characteristics (synapomorphies) of the order is the presence of phytomelanin, a black pigment present in the seed coat, creating a dark crust. Phytomelanin is found in most families of the Asparagales (although not in Orchidaceae, thought to be a sister to the rest of the group).

The leaves of almost all species form a tight rosette, either at the base of the plant or at the end of the stem, but occasionally along the stem. The flowers are not particularly distinctive, being 'lily type', with six tepals and up to six stamina.

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).

Reference: Wikipedia