Under the APG IV system of flowering plant classification, Asparagales are the largest order of monocots with 14 families,[5] 1,122 genera, and about 36,000 species, with members as varied as asparagus, orchids, yuccas, irises, onions, garlic, leeks, and other Alliums, daffodils, snowdrops, amaryllis, agaves, butcher's broom, Agapanthus, Solomon's seal, hyacinths, bluebells, spider plants, grasstrees, aloe, freesias, gladioli, crocuses, and saffron.

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.

The order is clearly circumscribed on the basis of molecular phylogenetics, but it is difficult to define morphologically since its members are structurally diverse.

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.

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 as with Yucca.

[11][12] The attribution of botanical authority for the name Asparagales belongs to Johann Heinrich Friedrich Link (1767–1851) who coined the word 'Asparaginae' in 1829 for a higher order taxon that included Asparagus[13] although Adanson and Jussieau had also done so earlier (see History).

The family Liliaceae was first described by Michel Adanson in 1763,[16] and in his taxonomic scheme he created eight sections within it, including the Asparagi with Asparagus and three other genera.

[18] Jussieu established the hierarchical system of taxonomy (phylogeny), placing Asparagus and related genera within a division of Monocotyledons, a class (III) of Stamina Perigynia[19] and 'order' Asparagi, divided into three subfamilies.

[21][22] In creating his scheme he used a modified form of Linnaeus' sexual classification but using the respective topography of stamens to carpels rather than just their numbers.

While De Jussieu's Stamina Perigynia also included a number of 'orders' that would eventually form families within the Asparagales such as the Asphodeli (Asphodelaceae), Narcissi (Amaryllidaceae) and Irides (Iridaceae), the remainder are now allocated to other orders.

[23] Meanwhile, the 'Narcissi' had been renamed as the 'Amaryllidées' (Amaryllideae) in 1805, by Jean Henri Jaume Saint-Hilaire, using Amaryllis as the type species rather than Narcissus, and thus has the authority attribution for Amaryllidaceae.

[24] In 1810, Brown proposed that a subgroup of Liliaceae be distinguished on the basis of the position of the ovaries and be referred to as Amaryllideae[25] and in 1813 de Candolle described Liliacées Juss.

[26] The literature on the organisation of genera into families and higher ranks became available in the English language with Samuel Frederick Gray's A natural arrangement of British plants (1821).

[28] The circumscription of Asparagales has been a source of difficulty for many botanists from the time of John Lindley (1846), the other important British taxonomist of the early nineteenth century.

In his first taxonomic work, An Introduction to the Natural System of Botany (1830)[29] he partly followed Jussieu by describing a subclass he called Endogenae, or Monocotyledonous Plants (preserving de Candolle's Endogenæ phanerogamæ)[30] divided into two tribes, the Petaloidea and Glumaceae.

By 1846, in his final scheme[31] Lindley had greatly expanded and refined the treatment of the monocots, introducing both an intermediate ranking (Alliances) and tribes within orders (i.e. families).

The number of known genera (and species) continued to grow and by the time of the next major British classification, that of the Bentham & Hooker system in 1883 (published in Latin) several of Lindley's other families had been absorbed into the Liliaceae.

An important addition to the treatment of the Liliaceae was the recognition of the Allieae[37] as a distinct tribe that would eventually find its way to the Asparagales as the subfamily Allioideae of the Amaryllidaceae.

The appearance of Charles Darwin's Origin of Species in 1859 changed the way that taxonomists considered plant classification, incorporating evolutionary information into their schemata.

The Darwinian approach led to the concept of phylogeny (tree-like structure) in assembling classification systems, starting with Eichler.

These various proposals to separate small groups of genera into more homogeneous families made little impact till that of Dahlgren (1985) incorporating new information including synapomorphy.

The establishment of major new clades necessitated a departure from the older but widely used classifications such as Cronquist and Thorne based largely on morphology rather than genetic data.

[57] This cladogram shows the placement of Asparagales within the orders of Lilianae sensu Chase & Reveal (monocots) based on molecular phylogenetic evidence.

[70] Numbers indicate crown group (most recent common ancestor of the sampled species of the clade of interest) divergence times in mya (million years ago).

[71] Acorales Alismatales Petrosaviales Dioscoreales 115 Pandanales 91 Liliales 121 Asparagales 120 Dasypogonaceae Arecales Poales Zingiberales Commelinales A phylogenetic tree for the Asparagales, generally to family level, but including groups which were recently and widely treated as families but which are now reduced to subfamily rank, is shown below.

[11][1] Orchidaceae Boryaceae Blandfordiaceae Lanariaceae Asteliaceae Hypoxidaceae Ixioliriaceae Tecophilaeaceae Doryanthaceae Iridaceae Xeronemataceae Hemerocallidoideae (= Hemerocallidaceae) Asphodeloideae (= Asphodelaceae) Xanthorrhoeoideae (= Xanthorrhoeaceae s.s.) Agapanthoideae (= Agapanthaceae) Allioideae (= Alliaceae s.s.) Amaryllidoideae (= Amaryllidaceae s.s.) Lomandroideae (= Laxmanniaceae) Asparagoideae (= Asparagaceae s.s.) Nolinoideae (= Ruscaceae) Agavoideae (= Agavaceae) Aphyllanthoideae (= Aphyllanthaceae) Brodiaeoideae (= Themidaceae) Scilloideae (= Hyacinthaceae) The tree shown above can be divided into a basal paraphyletic group, the 'lower Asparagales (asparagoids)', from Orchidaceae to Asphodelaceae,[74] and a well-supported monophyletic group of 'core Asparagales' (higher asparagoids), comprising the two largest families, Amaryllidaceae sensu lato and Asparagaceae sensu lato.

(Some members of Vanilloideae and Cypripedioideae have crustose seeds, probably associated with dispersal by birds and mammals that are attracted by fermenting fleshy fruit releasing fragrant compounds, e.g.

Members of the clade from Iridaceae upwards have infra-locular septal nectaries, which Rudall interpreted as a driver towards secondarily superior ovaries.

Stevens notes that most of its subfamilies are difficult to recognize, and that significantly different divisions have been used in the past, so that the use of a broadly defined family to refer to the entire clade is justified.

A separate paper accompanying the publication of the 2009 APG III system provided subfamilies to accommodate the families which were discontinued.