Editing Asparagales (section)

==Description==
[[File:Hippeastrum-seeds.jpg|thumb | [[Seed]]s of ''[[Hippeastrum]]'' with dark [[phytomelan]]-containing coat]]
[[File:Nolina Menton.JPG|thumb | Tree-like [[Habit (biology)|habit]] created by secondary thickening in ''[[Beaucarnea recurvata]]'']]

Although most species in the order are [[herbaceous plant|herbaceous]], some no more than 15&nbsp;cm high, there are a number of [[vines|climbers]] (''e.g.'', some species of ''[[Asparagus (genus)|Asparagus]]''), as well as several genera forming [[tree]]s (e.g. ''[[Agave]]'', ''[[Cordyline]]'', ''[[Yucca]]'', ''[[Dracaena (plant)|Dracaena]]'', ''[[Aloidendron]]'' ), which can exceed 10&nbsp;m in height. [[Succulent]] genera occur in several families (e.g. ''Aloe'').

Almost all species have a tight cluster of [[Leaf|leaves]] (a [[rosette (botany)|rosette]]), either at the base of the plant or at the end of a more-or-less woody [[plant stem|stem]] as with ''[[Yucca]]''. In some cases, the leaves are produced along the stem. The [[flower]]s are in the main not particularly distinctive, being of a general 'lily type', with six [[tepal]]s, either free or fused from the base and up to six [[stamen|stamina]]. They are frequently clustered at the end of the plant stem.

The Asparagales are generally distinguished from the [[Liliales]] by the lack of markings on the tepals, the presence of [[septal nectaries]] in the [[ovary (botany)|ovaries]], rather than the bases of the tepals or stamen filaments, and the presence of [[secondary growth]]. They are generally [[geophytes]], but with linear leaves, and a lack of fine [[reticular venation]].

The [[seed]]s characteristically have the external epidermis either obliterated (in most species bearing fleshy fruit), or if present, have a layer of black carbonaceous [[phytomelanin]] in species with dry fruits (nuts). The inner part of the seed coat is generally collapsed, in contrast to Liliales whose seeds have a well developed outer epidermis, lack phytomelanin, and usually display a cellular inner layer.

The orders which have been separated from the old Liliales are difficult to characterize. No single morphological character appears to be diagnostic of the order Asparagales.
* The flowers of Asparagales are of a general type among the [[lilioid monocot]]s. Compared to Liliales, they usually have plain [[tepal]]s without markings in the form of dots. If [[nectary|nectaries]] are present, they are in the [[septum|septa]] of the [[ovary (plant)|ovaries]] rather than at the base of the tepals or [[stamen]]s.
* Those species which have relatively large dry seeds have a dark, crust-like (crustose) outer layer containing the pigment phytomelan. However, some species with hairy seeds (e.g. ''[[Eriospermum]]'', family Asparagaceae ''s.l.''), berries (e.g. ''[[Maianthemum]]'', family Asparagaceae ''s.l.''), or highly reduced seeds (e.g. orchids) lack this dark pigment in their seed coats. Phytomelan is not unique to Asparagales (i.e. it is not a [[synapomorphy]]) but it is common within the order and rare outside it.{{sfn|ps=none|Chase|2004}} The inner portion of the seed coat is usually completely collapsed. In contrast, the morphologically similar seeds of Liliales have no phytomelan, and usually retain a cellular structure in the inner portion of the seed coat.<ref>{{Cite journal |last=Judd |first=Walter S. |date=1997 |title=The Asphodelaceae in the Southeastern United States |url=https://www.jstor.org/stable/41761540 |journal=Harvard Papers in Botany |volume=2 |issue=1 |pages=109–123 |jstor=41761540 |issn=1043-4534}}</ref>
* Most monocots are unable to thicken their stems once they have formed, since they lack the cylindrical [[meristem]] present in other angiosperm groups. Asparagales have a method of secondary thickening which is otherwise only found in ''[[Dioscorea]]'' (in the monocot order Disoscoreales). In a process called 'anomalous secondary growth', they are able to create new vascular bundles around which thickening growth occurs.{{sfn|ps=none|Rudall|1995}} ''[[Agave]]'', ''[[Yucca]]'', ''[[Aloidendron]]'', ''[[Dracaena (plant)|Dracaena]]'', ''[[Nolina]]'' and ''[[Cordyline]]'' can become massive trees, albeit not of the height of the tallest dicots, and with less branching.{{sfn|ps=none|Chase|2004}} Other genera in the order, such as ''[[Lomandra]]'' and ''[[Aphyllanthes]]'', have the same type of secondary growth but confined to their underground stems.
* [[Microsporogenesis]] (part of [[pollen]] formation) distinguishes some members of Asparagales from Liliales. Microsporogenesis involves a cell dividing twice ([[meiosis|meiotically]]) to form four daughter cells. There are two kinds of microsporogenesis: successive and simultaneous (although intermediates exist). In successive microsporogenesis, walls are laid down separating the daughter cells after each division. In simultaneous microsporogenesis, there is no wall formation until all four cell [[nucleus (cell)|nuclei]] are present. Liliales all have successive microsporogenesis, which is thought to be the primitive condition in monocots. It seems that when the Asparagales first diverged they developed simultaneous microsporogenesis, which the 'lower' Asparagales families retain. However, the 'core' Asparagales (''see'' [[#Phylogenetics|Phylogenetics]] ) have reverted to successive microsporogenesis.{{sfn|ps=none|Furness|Rudall|1999}}
* The Asparagales appear to be unified by a mutation affecting their [[telomere]]s (a region of repetitive [[DNA]] at the end of a [[chromosome]]). The typical '''Arabidopsis''-type' sequence of bases has been fully or partially replaced by other sequences, with the 'human-type' predominating.{{sfn|ps=none|Sýkorová|Lim|Kunicka|Chase|2003}}
* Other apomorphic characters of the order according to Stevens are: the presence of chelidonic acid, anthers longer than wide, tapetal cells bi- to tetra-nuclear, tegmen not persistent, endosperm helobial, and loss of mitochondrial gene ''sdh3''.{{sfn|ps=none|Stevens|2016|loc=[http://www.mobot.org/MOBOT/Research/APweb/orders/asparagalesweb.htm#Asparagales Asparagales]}}

According to [[Telomere|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''.