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 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 group

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
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
;Ginger-families
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
Suborder Strelitziineae Kress
Suborder Musineae Kress
Suborder Heliconiineae Kress
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.

Evolution

The common ancestor of the Zingiberales together with those of its sister order, the Commelinales, is estimated to have originated 158 Mya in the Early Cretaceous, with separation of the two orders between 80–124 Mya, and with rapid radiation into the major lineages in the mid Cretaceous ca. 60–100 Mya and six of the eight families established by the end of the Cretaceous, Estimates of crown group age vary widely between 34 and 110 Mya, and may need revision in the light of developing knowledge of the topology of the order.
Fossil-calibrated molecular estimates suggest a date of 110 to 80 Mya for the diversification of primary lineages. If Musaceae is the stem family of the order, as seems likely this places the origin of Zingiberales ca. 124 Mya, with diversification occurring ca. 110 Mya in the middle Cretaceous. That origin was congruent with the breakup of the southern land mass, Gondwana.
Probably the ancestral Zingiberales were distributed in tropical Gondwanal and encompassing present-day Americas, Africa, and Southeast Asia. Within this land mass, Australia seems the most likely anestral area, with subsequent dispersals between Africa and neotropical America. Earlier studies had implied Southeast Asia as the origin. The current distribution of the Zingiberales seems to be a product of numerous secondary and tertiary dispersal events between the major tropical regions of the world.
Zingiberales demonstrate an evolutionary trend in the ontogeny of the perianth. The appearance of a dimorphic perianth is variable throughout the commelinid monocots, with a transition from an undifferentiated monomorphic perianth to a dimorphic one occurring independently in the two sister orders, Commelinales and the Zingiberales. The evolution of floral morphology within Zingiberales demonstrates a marked correlation between the reduction of the number of fertile stamens, and increased petaloidy. The ancestral Zingiberales flower is thought to have had 5–6 fertile stamens, following which the staminode evolved in the lineage leading to Heliconiaceae+Zingiberineae, finally leading to 2–5 staminodia dominating the floral display.
The phylogenetic diversification and biogeographic dispersal of the Zingiberales was, in part, driven by the evolutionary radiation and diversification of their associated animal pollinators, which include bats, birds, non-flying mammals and insects. Six of the eight families of the Zingiberales contain taxa specialised for pollination by vertebrates, which appears to be the plesiomorphic state in the order. Of these six families two are exclusively vertebrate-pollinated. Pollination by insects also occurs in six families with one or possibly two families predominantly specialised for insect visitors.

Fossil record

Seed and fruit fossils of the Zingiberales appear in the Santonian of the Late Cretaceous, ca. 85 Mya, and thought to represent Musaceae and Zingiberaceae, but the place of the oldest Zingiberales fossil, Spirematospermum with its distinctive seeds remains uncertain, but is most likely Zingiberaceae. The leaf fossil record for Zingiberales also extends back to the Late Cretaceous. Other fossil records include rhizomes and phytoliths.

Diversity and biogeography

The four families of the basal banana group exhibit less taxonomic diversity than the terminal ginger group. The three genera of Musaceae are distributed in tropical Asia and Africa, although fossil evidence reveals their presence in North America and Africa in the Tertiary, while the three genera of Strelitziaceae are allopatric being found in Madagascar, southern Africa and the Amazon Basin respectively and Lowiaceae occurs in Southeast Asia. The largest family in this group, the Heliconiaceae is primarily neotropical, but also occurs in the Pacific from Samoa to Sulawesi.
Of the four Zingiberineae families, three are pantropical. The fourth, Cannaceae is restricted to the New World, although widely cultivated. This suborder contains the two largest families and the largest number of species.

Distribution and habitat

Zingiberales are pantropical and occur predominantly in the wet tropical regions of Asia, Africa, and the Americas, occupying nearly all tropical wet lowlands or middle elevation forests as part of the understory flora. In addition five genera from three of the Zingiberineae families, including Canna extend into subtropical and temperate regions. Of the eight families, Heliconiaceae, Marantaceae, and Costaceae are predominantly neotropical and Zingiberaceae most prevalent in Southeast Asian wet understory habitats. These are mainly small to medium-sized herbaceous taxa or vines. While some herbaceous Zingiberaceae such as Alpinia boia can attain a height of ten metres, only one species is a true canopy plant. The latter, a Madagascar endemic, has thick, palm-like trunks which push the fan-shaped crown of leaves up into the top layers of the forest. Some Zingiberales prefer a greater degree of light and are found in forest glades or margins, or in open secondary growth along streams and rivers.
The large family Zingiberaceae has a number of subfamilies, one of which, Zingiberoideae, has members that have adapted to Southeast Asia's monsoonal climates. They do so by becoming dormant in the dry season, which may last four to six months, shedding all above ground parts, existing only as underground fleshy underground rhizomes, some of which have starch rich tubers. With the onset of the wet season, they send up shoots and complete their life cycle during this time. Some taxa within Marantaceae, Costaceae, and Musaceae also occur in these habitats and have adapted in this way, but no Zingiberales occur in true desert regions.
In contrast some Zingiberales, including taxa from Marantaceae, Heliconiaceae, Cannaceae have adopted an aquatic habitat and are found along river margins, ponds, and swampy areas, with their rhizomes rooted underwater.

Ecology

Zingiberales forms a major component of tropical and subtropical ecosystems. Many of these plants have formed specialised pollination relationships with mammals, birds and insects through alterations in floral form.

Uses

Many Zingiberales are horticulturally important and grown as ornamental plants, e.g., Heliconia, Strelitzia, Maranta and Canna. Others are crop plants with culinary usage, e.g., Musa and Zingiber. Zingiberales also include sources of traditional medicines and spices, e.g. Alpinieae such as Elettaria and Amomum and galanga and Curcuma.

Books, symposium and chapters

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