Kindly sponsored by a member of the International Dendrology Society.
Julian Sutton (2022)
Sutton, J. (2022), 'Plagianthus divaricatus' from the website Trees and Shrubs Online (treesandshrubsonline.
Deciduous or semi-evergreen divaricating shrub, usually erect, to 2 m. Branchlets usually flexible and interlaced, densely to sparsely clad in stellate hairs at first, grooved; bark dark brown. Leaves alternate or in small fascicles on arrested branchlets. In young plants leaves linear- to spathulate-oblong, 2–3 cm × 3–5 mm, thin textured, more or less glabrous, midrib obscure; petioles ~3 mm. Leaves of adult plants linear-spathulate to narrow-obovate, 0.5–1.5(–2) cm × 0·5–2(–4) mm, more leathery and clad in stellate hairs, apex usually obtuse, midrib prominent; larger-leaved reversion shoots occur. Flowers unisexual, rarely hermaphrodite, to 5 mm diameter, axillary, solitary or in few-flowered cymes on arrested branchlets; peduncles and pedicels ~3 mm. Calyx campanulate, 2 mm diameter, with triangular teeth; corolla tube ~2 mm long, exserted; corolla lobes oblong, acute, yellowish; anthers 8–12, sessile on staminal tube; ovary 1(–2)-celled with 1 ovule per cell; stigma clavate or flattened. Fruit globose, ~5 mm diameter, densely clad in appressed stellate hairs, dehiscing irregularly from apex. Flowering September–November (New Zealand). (Allan 1961; New Zealand Plant Conservation Network 2022; Wagstaff & Tate 2011; Cullen et al. 2011).
Distribution New Zealand North, South, Stewart and Chatham Islands
Habitat By coasts and estuaries: saltmarshes and sandy or gravelly banks.
USDA Hardiness Zone 8-10
RHS Hardiness Rating H4
Conservation status Not evaluated (NE)
Unlike its tree-forming relative Plagianthus regius, few would see anything regal in this tough coastal shrub. With its mass of densely branching stems and small flowers, it is usually recommended in New Zealand on grounds of stress tolerance rather than beauty.
Plagianthus divaricatus spends its whole life as a divaricating shrub. The tangled, branched stems carry small narrow leaves rather sparsely, and may appear dark (Bean 1976) or silvery with stellate hairs (Southern Woods 2022), probably varying with growing conditions. In New Zealand gardens, both coastal and inland, it is grown as a free-standing mound in open, sunny situations, or trimmed into a hedge (Goughs Nurseries 2022; Tawapou Coastal Natives 2022). Bean (1976) described a quite different garden use in plant grown against a wall at Kew, where nowadays it would surely prove hardy without such protection, making ‘a graceful and distinct covering, developing into a thick tangle of dark slender stems, many of them pendulous and unbranching for more than a foot [~30 cm] of their length’. While essentially deciduous, cultivated plants may lose their leaves gradually, and it is sometimes billed as ‘semi-deciduous’ or ‘semi-evergreen’ by nurseries (Southern Woods 2022). At any rate, the density of its branching structure combined with the sparseness of its leaves means that it does not look very different in or out of leaf.
The inconspicuous flowers are held close to the branches, solitary or in few-flowered inflorescences, contrasting sharply with the large, much branched inflorescences of P. regius. Only the male flowers are sweetly scented (Wagstaff & Tate 2011). Flowers produce nectar and are attractive to bees (Akura Plant Nursery 2011) although formal pollination studies seem to be lacking.
A plant of diverse coastal and estuarine habitats, it is no surprise that experience in New Zealand gardens finds it tolerant of salinity, waterlogging and coastal exposure, although moist soil is not a prerequisite (Goughs Nurseries 2022; Southern Woods 2022). Its cold hardiness in gardens is more unexpected. Grown in New Zealand even well inland (Tawapou Coastal Natives 2022), trials in France’s Loire Valley found it surviving –15°C (Harris, Cadic & Decourtye 1998). Further north in Europe, a plant at RBG Edinburgh died back by one third to about 60 cm in height during the severe winter of 1879–80 (local minimum –17°C) and resprouted readily (Gorrie 1883).
Plagianthus divaricatus was among the first New Zealand plants described scientifically, by Johann and Georg Forster, father-and-son scientists on James Cook’s second (1772–1775) voyage (Forster & Forster 1776). Its first introduction to cultivation outside New Zealand was to Kew, by the British plant collector Allan Cunningham; it had flowered by 1833 (Hooker 1833). This must have been one of the first divaricating shrubs seen in Europe, and its relationships were still unclear. Cunningham’s only trip to New Zealand was in the summer of 1826–7 (le Lièvre 1988), so the date 1820 given by Edwards & Marshall (2019) seems too early. It had flowered at the Vilmorin nursery near Paris by 1851 (Bean 1976).
Apparently unknown in North American cultivation, P. divaricatus remains a rare, parenthetic plant in Europe. Plants are recorded from Logan Botanic Garden, and in an area away from public view at RBG Edinburgh; neither is of known wild provenance (Royal Botanic Garden Edinburgh 2022). There is a plant of wild provenance at Plantentuin Universiteit Gent, Belgium (Plantcol 2022). Perhaps the first word on its horticultural merits might also be the last: ‘It is indeed a shrub that has little to recommend it on the score of beauty, but much from its rarity and structure’ (Hooker 1833). Little has changed.