Plagianthus regius (Poit.) Hochr. subsp. chathamicus (Cockayne) de Lange
Lowland Ribbonwood, Manatu, Ribbonwood, Riverbank Ribbonwood Plagianthus regius (Poit.)
Hochr.
Plagianthus regius (Poit.) Hochr. subsp.
chathamicus (Cockayne) de Lange
Plagianthus divaricatus J.R. Forster & G.
Forster
Plagianthus ×cymosus T.Kirk
Plagianthus is a genus with the family Malvaceae. The 2 species of Plagianthus are endemic to New Zealand (and the Chatham Islands). These are vernacularly known as ribbonwoods, a name which they share with species of the closely related (and fellow New Zealand endemic) genus Hoheria. Ribbonwoods are deciduous shrubs or trees, bearing small white or yellow-white flowers in late spring, followed by pendulous seeds.
It is distinguished from Hoheria by the presence of smaller flowers with linear stigmas and solitary carpels. (Hoheria has clusters of 5 or more carpels.)
The genus name is a reference to the petals of a Plagianthus flower not being all the same size.
The genus Plagianthus, as currently recognised, is endemic to New Zealand and the Chatham Islands, and consists of 2 species - the saltmarsh ribbonwood, Plagianthus divaricatus and the lowland ribbonwood, Plagianthus regius. It was introduced by J.R. and G. Forster for the former species. The latter species was first described by Poiteau, as Philippodendrum regium Poit., based on specimens raised from seed erroneously recorded as being collected from Nepal [1].
In the past various authors have included species of Hoheria, and the Australian endemic genera Asterotrichion, Lawrencia and Gynatrix. Plagianthus linariifolia Buchanan is Coprosma rugosa Cheeseman, and belongs in Rubiaceae [2]. Plagianthus humilis Blanco is Munronia humilis (Blanco) Harms, and belongs to the Meliaceae.
Plagianthus does not have the typical aspect of a mallow, either in habit or flower, and its familial placement was initially uncertain. Poiteau placed his Philippodendrum close to Dombeyaceae and Byttneriaceae (treated here as subfamilies Dombeyoideae and Byttnerioideae of family Malvaceae), and subsequent authors treated it as the type of family Philippodendraceae, subfamily Philippodendroideae or tribe Philippodendreae. Hooker placed Plagianthus divaricatus in Euphorbiaceae, but considered an alternative placement in Bombacaceae (treated here as subfamily Bombacoideae of family Malvaceae.
The genus was subsequently recognised as belonging to the tribe Malveae, and as the titular member of the Plagianthus alliance, consisting of Plagianthus, Hoheria, Asterotrichion, Lawrencia and Gynatrix. Recent DNA sequencing has confirmed this grouping, and placed it, with the South American genus Sidasodes and two or three species of the polyphyletic genus Sida, as the sister group to the remainder of subtribe Abutilinae [3]. A case could be made for resurrecting subtribe Plagianthinae for this slightly expanded grouping.
The two species hybridise where they come into contact, e.g. on the banks of tidal rivers, giving rise to Plagianthus ×cymosus T.Kirk.
Plagianthus regius (Poit.) Hochr.
Plagianthus regius (Poit.) Hochr. subsp. chathamicus (Cockayne)
de Lange Lowland Ribbonwood, Manatu, Ribbonwood, Riverbank Ribbonwood
Plagianthus regius is found over most of New Zealand, including Stewart Island and the Chatham Islands, but is absent from North Cape and Ninety Mile Beach in the far north. It grows in riparian habitats from sea level to 1500 ft, preferring moist soil.
It has distinct seedling, juvenile and adult forms.
The seedling form has an erect habit, and foliage similar to the adult form, but with truncate or cordate leaf bases.
The juvenile form (except in subsp. chathamicus) is a dense bush of slender, interlaced, branches. The leaves are ovate, 5-15mm × 3-10mm, and serrated.
In its adult form it is New Zealand's largest deciduous tree, reaching 50 ft in height. The adult form, in its earlier stages, is a graceful, small to medium tree, reminiscent in habit of a Silver Birch. (Hence, presumably, the synonym Plagianthus betulinus.) When older it becomes broader and bulkier. (A specimen growing in an open location in Christchurch has a spread of 15m, and a trunk with a diameter of 1m.)
The foliage consists of ovate to ovate-lanceolate, toothed, leaves, from 1"-2½" long, and ¼"-2" wide, with a covering of stellate hairs on both surfaces. The yellowish-white flowers are small, but occur in large, tomentose, terminal panicles, in late spring. The calyx is campanulate. The petals are linear-oblong (narrower in male than in female flowers) and rounded at their tips. The staminal tube is long and slender, in the male flowers protuding beyond the petals, and bears many short-stalked anthers. The fruit is a small, ovoid, single-seeded, capsule, which on maturity splits down one side.
The population on the Chatham Islands is classified as subsp. chathamicus. It is distinguished by a non-divaricating habit (i.e. non-interlaced branches) in the juvenile form.
Synonyms of Plagianthus regius include Philippodendron regium Poit., Plagianthus betulinus A.Cunn. and Plagianthus urticinus A.Cunn..Synonyms of Plagianthus regius ssp. chathamicus include Plagianthus betulinus var. chathamicus (Cockayne) Cockayne and Plagianthus chathamicus Cockayne.
Plagianthus divaricatus J.R. Forster
& G. Forster Makaka, Runa, Saltmarsh Ribbonwood, Shore Ribbonwood, Swamp Ribbonwood
A spreading deciduous bushy shrub, growing to 8ft in height, and 12ft in width, to be found in saltmarsh and swamp habitats, over the whole of New Zealand, including those regions of the far north from which Plagianthus regius is absent. Like Plagianthus regius it has distinct juvenile and adult forms.
The juvenile form has 2-3.5cm long linear or spathulate leaves.
The adult form has 0.5-2 cm long linear, spathulate or narrow obovate, dark green, leaves. It bears very fragrant, small, yellowish-white tubular flowers, with 8-12 stamens, borne, solitarily or in small clusters, in leaf axils, in late spring. The glabrous calyx is hemispherical in form. The fruit is a small, downy, capsule containing 1 or 2 seeds, on maturity bursting irregularly.
Napaea divaricata Alef. is a synonym of Plagianthus divaricatus.
Plagianthus ×cymosus is a hybrid between Plagianthus divaricatus and Plagianthus regius. It commonly occurs along the banks of tidal rivers where its parents come into contact, but has been recorded in the absence of one or both parents.
It is recorded from the valley of the McLennan River (Otago) [4], along the banks of the Pelorus River (Marlborough) [5], near Kaitaia in the Auckland Peninsula [6, 7], from the Miramar Peninsula [8], from the banks of Waihopai River (near Invercargill) [9, 7], the Chatham Islands [10], the vicinity of Dunedin [7] and the region of the Marlborough Sounds [7]. A record from the Bank's Peninsula [11] may have been a flowering plant of the juvenile form of Plagianthus regius [12].
Cytology
Both species of Plagianthus have diploid chromosome counts of 42, as does subsp. chathamicus.
Images
Phytophagous Insects
Oleander Scale, Aspidiotus nerii Bouché, and Greedy Scale, Hemiberlesia rapax (Comstock) Ferris, are recorded on Plagianthus divaricatus in New Zealand.
Pathogens
The rust fungus Puccinia plagianthi McAlpine (aka Puccinia hoheriae) infects all species of Hoheria and Plagianthus [], and also the Australian species Gynatrix pulchella [] and Asterotrichion discolor. It causes leaf spotting and stem distortion, and can be diagnosed by the presence of irregular pale yellow, grey or brown blotches on both surfaces of green leaves or on distorted sections of the stem, by the presence of dark brown pustules (telia) (less than 2mm in diameter) on the lower surface of the leaves, either clustered in the blotches or scattered singly.on leaf surfaces, and by the presence of yellow spots (pycnia) on both surfaces of green leaves. Unlike many rust fungi Puccinia plagianthi does not (as far as is known) have an alternate host. It is not considered of economic importance, and control measures are not necessary. []
References
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© 2002, 2003, 2004, 2005, 2008 Stewart Robert Hinsley