Zingiberales


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 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 "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, most likely in Australia, and diverged relatively rapidly with the families as they are known today established by the end of the period. Zingiberales are found throughout the tropics 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, food crops, spices and traditional medicines.

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. Venation pinnate-parallelodromous, with midrib, 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, 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.
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 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 are considered to be specialised isomorphic root hair cells, penni-parallel leaf venation, supervolute ptyxis, 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 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 placed the Scitamineae as an Ordo of the Epigynae alliance in the monocotyledons, incorporating both of Grisebach's families. Later systems such as the Engler system and the Wettstein system, also considered Scitamineae as a monocotyledon order and were influential for a long period of time. Variants included Scitaminales. Hutchinson, although initially using Scitamineae, later followed Takenoshin Nakai. in adopting Zingiberales as the name for the order in Division Calyciferae, although credit is generally given to Nakai. This usage was followed by Takhtajan within superorder Lilianae and by Dahlgren 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.

Modern era

Using molecular phylogenetics, which was first applied to the order in 1993, the Angiosperm Phylogeny Group system, 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 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, 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, Musaceae, Heliconiaceae, Strelitziaceae, Costaceae, Cannaceae, Marantaceae, and Lowiaceae. The APG II system provided a classification of families for the first time, retaining Kress's eight families.
;Families
  • order Zingiberales Griseb.
  • * family Cannaceae Juss.
  • * family Costaceae Nakai
  • * family Heliconiaceae Vines
  • * family Lowiaceae Ridl.
  • * family Marantaceae R.Br.
  • * family Musaceae Juss.
  • * family Strelitziaceae Hutch.
  • * family Zingiberaceae Martinov
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 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 or develop as an infertile staminode. 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 somewhat uncertain;
;Ginger-families
  • Zingiberaceae, Costaceae, Cannaceae, Marantaceae. A monophyletic derived terminal clade with the number of fertile stamens reduced to one or to one half, with a single theca. The remaining components of the androecium develop as four or five elaborate petaloid staminodia, highly modified from sterile stamens. This group may have one or two but assume the structure and function of petals as pollinator attraction. This group demonstrate complex patterns of fusion among their floral organs including the staminodes. In Zingiberaceae and Costaceae the staminodes fuse to form a staminodial labellum which provides much of the floral display. In general the flowers of this group display higher degrees of organ fusion and specialisation.

    Phylogeny

Using combined morphology and molecular data, Kress and colleagues confirmed the broad separation into two clades based on morphology alone, and produced an infraordinal structure. In this scheme, they divided the families of the order as follows, with the ginger group as one suborder, and the banana group divided amongst three separate suborders:
Suborder Zingiberineae Kress
  • Superfamily Cannariae Kress
  • * Cannaceae A.L. Jussieu
  • * Marantaceae Petersen
  • Superfamily Zingiberariae Kress
  • * Costaceae Nakai
  • * Zingiberaceae Lindley
Suborder Strelitziineae Kress
  • * Lowiaceae Ridley
  • * Strelitziaceae Hutchinson
Suborder Musineae Kress
  • * Musaceae A.L. Jussieu
Suborder Heliconiineae Kress
  • * Heliconiaceae Nakai
While the two sister family groups that constitute the Zingiberineae and also the basal Strelitziineae sister group were strongly supported, the position of Musaceae and Heliconiaceae were not. In the above model, Musaceae appears as the first branching family, and Heliconiaceae placed as sister to the Zingiberineae. Other studies placed these and the Strelitziaceae-Lowiaceae sister group in a trichotomy with the remaining families. While a revision of the first model placed Heliconiaceae as the first branching lineage with Musaceae in a sister relationship with Strelitziineae, which in turn was sister to Zingiberineae. A third model supports Musaceae as the basal group but places Heliconiaceae as sister to Strelitziineae. The failure to resolve the ancient rapid divergences of this order with multi-gene phylogenies and plastid data has important implications for understanding the evolution of characteristics.
Finally in 2016 Sass and colleagues, using multiplexed exon capture were able to resolve the entire phylogenetic tree with high support. This confirmed the place of Musaceae as sister to the remaining families, confirming Model 3.