Pandanales

▪ plant order

Introduction

      diverse order of the monocotyledon (monocot) group, whose 1,345 species range from large arborescent plants of rainforests and coastal areas in the tropics to twining herbs (spice and herb) and lianas (liana), as well as minute, saprophytic herbs of the forest floor. The order is made up of five families: Pandanaceae (screw pine family), Cyclanthaceae (Panama hat plant family), Triuridaceae, Stemonaceae, and Velloziaceae.

Pandanaceae

      The four genera of the family Pandanaceae— pandanus (screw pine), Freycinetia, Sararanga, and Martellidendron—are distributed in coastal or marshy areas in the tropics and subtropics of the Old World (Paleotropics). They are abundant in the Malay Archipelago, Melanesia, and Madagascar and have a few species in Hawaii, New Zealand, southern China, and Japan.

 Fibre from the leaves and roots of the screw pine is used for mats, baskets, cording, and fishing nets. A few species (P. leram, P. andamanensium, and P. utilis) have edible starchy fruits (fruit). Leaves of the most common species, P. odoratissimus, are used to make an Indian perfume and flavouring (kewra attar) popular in Southeast Asia. Several are ornamentals, including P. veitchii, which is appreciated for its dark green glossy leaves with silvery white borders, and Freycinetia banksii, which is trained to grow around peat-covered pillars in New Zealand.

      In Pandanaceae the spiral ranks of leaf bases that are pressed closely together are distinctive. The leaves are alternate and arranged in three rows, except in Sararanga, where they are arranged in four. The leaf sheath is not well differentiated except in Freycinetia, and petioles are absent. The simple leaf blades are very long and narrow and usually leathery and rigid, with fibrous spines along the margins and midrib. silica has not been observed in the family, but calcium oxalate is abundant as raphides and other crystalloid forms. Cyanogenic compounds are reported in some species of screw pine.

      Pandanus, Martellidendron, and Sararanga are dioecious. Freycinetia was long thought to be dioecious, but bisexual inflorescences (inflorescence) have been discovered in F. reineckei in Samoa.

      Pandanus, a genus of about 700 species, occupies many habitats. Its species occur along seashores and lagoons, in mangrove fringes and lowland swamps, along rivers, in mountain forests, and in shady forests, where they may be understory shrubs. They represent a diversity of growth forms. Many are trees, reaching up to 20 metres (about 65 feet) with leaves 5 metres (16 feet) or longer. Most species have large stilt roots that support the trunk. The stem terminates in several equal branches, each of which ends in a dense crown of leaves. Coastal species often have spreading branches supported by lateral roots. Such branches may separate and form new individuals in a kind of vegetative reproduction.

      The genus is thought to be pollinated by the wind; however, white to pink spathes enclose the inflorescences, and an odour is known to be emitted from some inflorescences (such as P. odoratissimus), and so insects or animals probably pollinate the flowers to some degree. Animals and sea currents disperse the yellow, pink, or red drupes (drupe).

      Freycinetia is found from Sri Lanka through Southeast Asia to northern Australia, Polynesia, and New Zealand. The woody plants climb by means of flattened, often long and wiry roots. Their leaves, which are less than 2 metres (6.5 feet) long, are linear, obovate (the widest axis above the middle), or ovate (the widest axis below the middle) in shape. They have membranous earlike appendages near the base and spiny margins, at least near the tip.

      The inflorescence in Freycinetia is a terminal spadix, usually borne in groups of three but rarely solitary. The spadix bears several bracts; the lower ones are leaflike, and the next higher are variously coloured (orange, pink, salmon, red, yellow, lavender). The uppermost are often fleshy and edible, containing hexose (sugar). Female spadices bear single or united carpels, and the males bear densely crowded stamens, each with a minute filament, a globose, linear, or oblong anther, and a blunt tip. No perianth is evident at maturity in either male or female flowers. The stamens and pistils are so closely crowded that definition of single flowers is very difficult.

      Pollination of Freycinetia by birds and bats has been reported in Indonesia, Samoa, Hawaii, and New Zealand. Bats and birds are attracted by the edible bracts and by the pollen that is borne in a waxy matrix of edible oils.

      The genus Sararanga has only two species: S. sinuosa, native to New Guinea, the Solomon Islands, and the Admiralty Islands, and S. philippinensis, native to the Philippines. The plants grow inland in mountain forests and on woody slopes near the sea. Both species are trees with long, narrow leaves. The inflorescences are pendant and borne in panicles, and the flowers have a cupule apparently representing a perianth. The greenish white inflorescences are assumed to be wind-pollinated.

      Martellidendron contains seven known species—six native to Madagascar and one endemic to the Seychelles islands in the mid-Indian Ocean. The genus was formerly included in the more widespread Pandanus, but molecular studies have shown it to be distinct from that genus and morphologically separable as well.

Cyclanthaceae

      The family Cyclanthaceae, with 12 genera and 225 species, is restricted to the New World tropics (Neotropics), extending from southern Mexico through Central America, the West Indies, and central Bolivia and southeastern Brazil in South America. Most of the family is centred in Colombia, where two endemic genera are found.

      The family includes herbaceous or slightly arborescent plants and a few lianas. Because their leaves are plicate (fanlike), the Cyclanthaceae are often considered to be related to palms (palm), but there are developmental differences in the leaves of the two families, and the similarities are due to convergent or parallel evolution.

      In the Cyclanthaceae the arrangement of leaves is spiral or rarely distichous. Petioles are universally present and may be long (as in Carludovica palmata, the Panama hat plant) or short. The blade is always plicate and varies from entire and small (Ludovia and Pseudoludovia) to bifid or palmately split (Panama hat plant). There are usually one to three major ribs (costae), but the genus Cyclanthus has strongly bifid leaves in which the central costa divides near the base, each branch running to the tip of its segment.

 The young leaves of Carludovica palmata have long been used for making Panama hats. Ecuador, where the species is widely cultivated for the fibres known as “toquilla straw,” exports more than a million of these hats each year. Older leaf fibres are used to make mats and baskets. Other uses include the making of brooms in Guyana from leaves of C. sarmentosa and thatching in Peru using the leaves of C. angustifolia.

      The inflorescence of the Cyclanthaceae varies in shape from more or less spherical to long-cylindrical and bears two to four or eight spathes that differ in size and may be red, white, yellow, or green in colour. The plants are monoecious, each bearing both male and female flowers. In all but one genus (Cyclanthus), the flowers are borne in sessile groups of a female flower surrounded by four males. The groups are closely appressed in a spiral from the base to the apex of the spadix.

      The spadix of Cyclanthus is unusual both in the family and in monocotyledons as a whole. Male flowers, consisting of single stamens, are in four rows in a cycle around the spadix. The female flowers consist of ovaries, which are fused into female cycles, alternating with the male cycles and separated from them by thin wings, which are thought to represent perianth members.

      Many of the species of Cyclanthaceae grow on riverbanks and a few in mangrove communities along coasts. A strong scent produced by the flowers attracts weevils (weevil), which appear to be the pollinators. Heat is also produced by the inflorescences, and the coloured spathes probably serve as attractants. Dispersal of seeds is largely by ants (ant), which visit the fruiting inflorescences. Seeds of the riverside species are probably dispersed by water, although birds, mammals, and other animals may also be involved.

Triuridaceae

      The American botanist Arthur Cronquist suggested in the early 1980s that Triuridaceae may eventually become established as a separate subclass, but DNA analysis at the close of the 20th century recognized members of this family as being closely related to the Pandanaceae and Cyclanthaceae families, although they are distinctive in many physical ways.

      The family Triuridaceae differs from the other members of order Pandanales in being small, achlorophyllous, saprophytic herbs with reduced scalelike leaves and rather small flowers. Members of this family are found in tropical areas around the world and include eight genera and about 48 species.

      The leaves of Triuridaceae are small and scalelike with a triangular to ovate shape. There are usually few leaves on the stem, and these probably are unimportant to the plant. They generally have unisexual flowers with 3 to 10 somewhat basally fused perianth parts in one or two series. There are typically three or six stamens fused to the perianth. Many separate or basally united carpels develop over a flat to globose receptacle.

      Little is known about the pollination of Triuridaceae, although it is probably accomplished by some insect vector since the flowers have attractive structures and emit a fragrance.

      Triuridaceae have developed a symbiotic relationship with mycorrhizal fungi (fungus) and live on the forest floor of tropical rainforests. The fungal mycelium (body) penetrates the root hairs and other epidermal cells of the plant. The fungi absorb organic matter and nutrients from the substrate and enzymatically convert them into substances that the vascular plant can use.

Stemonaceae

      The family Stemonaceae, with four genera and 27 species, consists of herbs and vines in both tropical and temperate zones. The Stemonaceae are herbs, vines, or shrublets with rhizomes or tubers and petiolate leaves with entire blades. The flowers are usually bisexual and dimerous or tetramerous with four tepals, four stamens, and two carpels. Although formerly associated with the yam family, Dioscoreaceae (order Dioscoreales), they now are considered to be allied to the Cyclanthaceae and Pandanaceae families.

Velloziaceae

      The predominantly woody shrubs of the family Velloziaceae (nine genera and 240 species) are found primarily in the drier parts of South America (with an outlier in Africa).

      Velloziaceae can be herbs, but the most conspicuous members are woody shrubs, often with dichotomous branching. The leaves are linear with parallel venation and sometimes possess spiny margins. The flowers are typically trimerous and sometimes possess “coronal appendages” on the tepals. Formerly the Velloziaceae was associated with the Neotropical Bromeliaceae (order Bromeliales). The highest diversity of this family occurs in rocky outcrops of interior mountain ranges in southeastern Brazil.

Paul E. Berry

* * *