Zingiberiflorae

The Zingiberales are flowering plants forming one of four orders in the commelinids clade of monocots, together with its sister order, Commelinales. The order includes 68 genera and 2,600 species. Zingiberales are a unique though morphologically diverse order that has been widely recognised as such over a long period of time. They are usually large herbaceous plants with rhizomatous root systems and lacking an aerial stem except when flowering. Flowers are usually large and showy, and the stamens are often modified ( staminodes) to also form colourful petal-like structures that attract pollinators.

Zingiberales contain eight families that are informally considered as two groups, differing in the number of fertile stamens. A " banana group" of four families appeared first and were named on the basis of large banana-like leaves. Later, a more genetically coherent ( monophyletic) " ginger group" appeared, consisting of the remaining four families. The order, which has a fossil record, is thought to have originated in the Early Cretaceous period between 80 and 120 million years ago (Mya), most likely in Australia, and diverged relatively rapidly with the families as they are known today established by the end of the period (66 Mya). Zingiberales are found throughout the tropics (pantropical) with some extension into subtropical and temperate climates. They rely on insects for pollination, together with some birds and small animals.

The order includes many familiar plants, and are used as ornamental plants ( Bird of Paradise flower, heliconias, prayer-plants), food crops ( bananas, plantains, arrowroot), spices and traditional medicines ( ginger, cardamom, turmeric, galangal, fingerroot and myoga).

Description

Zingiberales are one of an ecologically and morphologically diverse and species-rich order of monocots, with one of the most distinct floral morphology. They are large rhizomatous herbaceous plants but lacking an aerial stem, except when flowering.

Leaves usually petiolate with distinct petiole and lamina, leaf arrangement distichous (spiral in Musaceae). Venation pinnate-parallelodromous, with midrib (midvein), S-shaped lateral veins and fine transverse venation.

Flowers are generally large and showy, following the general monocot pattern, with inflorescences in thyrse-like spikes, zygomorphic to asymmetric, with two trimerous whorls of tepals. Gynoecium tricarpellate, ovary epigynous (inferior), two trimerous androecial whorls with stamens 6, 5 or 1. Stamens have elongated sterile filaments to which are attached anthers, distally, comprising about half of the length of the total stamen. Septal nectaries often present. Pollen sulcate but often inaperturate (lacking apertures).

Fruit capsular or schizocarp. Phytochemistry: Often containing raphides,

Specific characteristics which help to distinguish this order include a herbaceous arborescent stem, distichous phyllotaxy, large petiolate leaves in which the petioles are often long, parallel and transverse venation diverging laterally from a prominent common midrib, and inflorescences of conspicuous colorful bracts (bracteate inflorescence) and the substitution of one to five rudimentary staminodia for fertile stamens.

Leaf architecture is useful for distinguishing families within Zingiberales, based on vein pattern type, vein length per area, and other aspects of vein architecture such as angle of vein divergence, with three main types of venation recognised. These are the ''Zingiber''-type, with square to vertically elongate areoles, the ''Costus''-type, with horizontally elongate areoles and the ''Orchidantha''-type with cross veins spanning multiple parallel veins.

Apomorphies

The apomorphies (derived characteristics common to a taxonomic group) are considered to be specialised isomorphic root hair cells, penni-parallel leaf venation, supervolute ptyxis (left and right halves of immature leaf lamina rolled into each other), diaphragmed air chambers in leaves and stem, presence of intracellular silica bodies, epigynous flowers and an inferior ovary, pollen grains without distinctive aperture but with a reduced exine layer and an elaborated intine layer, nuclear endosperm development, and arillate seeds.

Taxonomy

''"The Zingiberiflorae, whether treated as a separate superorder, as here, or an order in a more widely circumscribed unit, is one of the most indisputably natural suprafamilial groups."''

History

The Zingiberales have always been considered a unique and coherent ( monophyletic) group, although accounting for <4% of extant monocots, which has led some authors to suggest they should constitute a higher taxonomic rank than order. For a brief history of the taxonomy of this order, see Scitamineae, and Kress 1990. They were first described by August Grisebach, their botanical authority, in 1854 as Zingiberides, an order of monocotyledons, subdivided into two families, Scitamineae and Musaceae.

Based on morphological grounds alone, early systems, such as Bentham and Hooker (1883) placed the Scitamineae as an ''Ordo'' (family) of the Epigynae alliance in the monocotyledons, incorporating both of Grisebach's families. Later systems such as the Engler system (1903) and the Wettstein system (1924), also considered Scitamineae as a monocotyledon order and were influential for a long period of time. Variants included Scitaminales (Warming 1912). Hutchinson (1926), although initially using Scitamineae, later followed Takenoshin Nakai (1930). in adopting Zingiberales as the name for the order (6 families) in Division Calyciferae, although credit is generally given to Nakai. This usage was followed by Takhtajan (1966) within superorder Lilianae and by Dahlgren (1985) in its own superorder Zingiberiflorae.

In contrast the Cronquist system retained Scitamineae as the name for this order with eight families, but organised the order in the subclass Zingiberidae of the class Liliopsida (monocotyledons).

Modern era

Using molecular phylogenetics, which was first applied to the order in 1993, the Angiosperm Phylogeny Group (APG) system (1998), (which generally followed Dahlgren, but with less divisions) confirmed the position of Zingiberales as a monophyletic order within the monocots, placing it in the commelinoid clade, as sister group to Commelinales, which Dahlgren had treated within a separate superorder. This was an ordinal system that did not examine subordinal structure. The 2003 revision (APG II) changed commelinoid to commelinid, but not the relationships, and this remained unchanged in the subsequent 2009 APG III system and 2016 APG IV system without addressing interfamilial relationships.

Subdivision

The order, which now has more than 2,600 species, distributed in 68 genera over eight families, has been subdivided from early times. In the Bentham & Hooker system (1883), their Ordo Scitamineae had four tribes: Zingibereae, Maranteae, Canneae, and Museae. These have become progressively divided to form the modern phyletic classification into the following monophyletic families: Zingiberaceae (gingers), Musaceae (bananas), Heliconiaceae (heliconias), Strelitziaceae (bird-of-paradise), Costaceae (spiral gingers), Cannaceae (canna lilies), Marantaceae (prayer plants), and Lowiaceae (Orchidantha). The APG II system (2003) provided a classification of families for the first time, retaining Kress's eight families.

;Families (genera/species)
* order Zingiberales Griseb.
** family Cannaceae Juss. (1/10 '' Canna'' cannas)
** family Costaceae Nakai (7/143 ''e.g.'' '' Costus'' spiral gingers)
** family Heliconiaceae Vines (1/194 ''Heliconia'' heliconias)
** family Lowiaceae Ridl. (1/18 ''Orchidantha'')
** family Marantaceae R.Br. (29/570 ''e.g.'' '' Maranta'' prayer plants)
** family Musaceae Juss. (3/91 ''e.g.'' ''Musa'' bananas)
** family Strelitziaceae Hutch. (3/7 ''e.g.'' '' Strelitzia'' birds of paradise)
** family Zingiberaceae Martinov (50/1,600 ''e.g.'' ''Zingiber'' gingers)

Based on morphology alone, the Zingiberales have been considered to form two main groups, each with four families, utilising the number of fertile stamens;

;Banana-families
* Musaceae, Strelitziaceae, Lowiaceae, Heliconiaceae. A paraphyletic basal assemblage with 5 or (rarely) 6 fertile stamens at maturity, arranged in as trimerous inner and outer whorls. In those with five stamina, the sixth may regress and be absent (Strelitziaceae and Lowiaceae, some Musaceae) or develop as an infertile staminode (Heliconiaceae, some Musaceae). Petals and stamens are often fused at the base to form a floral tube. These are known as the banana-families or the bananas on the basis of large banana-like leaves. For this reason these four families were previously all included in Musaceae, but the exact relationship between them remains some what uncertain;

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