New Zealand’s native brooms: Overlooked treasures? Murray Dawson1 New Zealanders typically think of they must be chipped or otherwise broom plants growing in the wild as treated – to enable them to germinate. rampant weeds, because they are New Zealand’s native brooms all so familiar with the widespread and belong to the genus Carmichaelia. exotic common (or Scotch) broom, 23 out of 24 currently recognised Cytisus scoparius (Fig. 1A–C), and species of Carmichaelia are endemic to the Montpellier broom, Genista New Zealand – that is to say, they are monspessulana, which are invasive unique to this country (Table 1)2. Native in disturbed and sunny areas such brooms are found from the Far North to as riversides, forest tracks and open Stewart Island in a variety of habitats, hillsides. These infested areas are from coastal to alpine. The proliferation blanketed in seas of bright yellow of morphologically diverse but closely flowers, followed by pods that related species in Carmichaelia is a explosively disperse seed several good example of adaptive radiation metres in all directions. Branches of in the New Zealand flora – the rapid European species were traditionally diversification of species to occupy used for sweeping which explains the ecological niches – as found elsewhere, common name “broom”. for example, in our native Coprosma In comparison, New Zealand’s native A and Veronica (hebes). brooms contain some remarkable Although Carmichaelia is distributed rarities that should not be tarred throughout New Zealand, many are with the same brush as their weedy threatened, including a high proportion European cousins. Make no mistake – of species restricted to drier eastern our native brooms are treasures with a areas of the South Island. Most wide range of interesting growth forms New Zealand native brooms prefer ranging from prostrate shrubs (only disturbed and open habitats which 2 cm tall) to spectacular trees (up to mean they are vulnerable to erosion 10 m). They are predominantly leafless and being out-competed by weeds in and are able to photosynthesise the lowlands. Furthermore, our native through flattened or cord-like stems brooms are highly palatable to a wide called cladodes. Most native species array of browsing animals, ranging have purple flowers, although colour in size from rabbits and hares up to varies from pale lavender through to possums, sheep, goats and deer – all intense pink – creamy white or yellow of the introduced herbivores seem to flowers are much less common. munch them! Several native brooms make excellent garden subjects and deserve to be B Because of their high conservation more widely grown. Most native brooms values, native brooms should not be are very hardy when planted in full sun removed from the wild. Unfortunately, and free-draining soils and few tolerate some plants (such as the Canterbury heavy shade and high humidity. pink broom, Carmichaelia torulosa) have accidentally been killed in the wild Along with native species including by herbicide spraying through being kakabeak (Clianthus spp.) and kōwhai confused for the weedy exotic brooms. (Sophora spp.), brooms belong to the legume family Fabaceae, which is why In this article, I will provide an overview they have pea-like flowers. Legumes fix of this remarkably diverse native atmospheric nitrogen through special C plant group, covering all low growing root nodules and therefore cope well species, and a selection of shrub and Fig. 1 Cytisus scoparius growing as a weed in poorly developed soils. Their seeds on Banks Peninsula, Canterbury. A, plant still tree species suitable for cultivation. usually have very hard seed-coats that in flower mid-winter. B, close-up of flower. If you are interested in growing need to be scarified – in other words, C, close-up of old twisted pods that have New Zealand’s native brooms, there is ejected their seeds. Photos: Murray Dawson. a good range available from specialist native plant nurseries. 1 Landcare Research, PO Box 69040, Lincoln 7640, New Zealand; [email protected] 2 The remaining species, Carmichaelia exsul, is endemic to Lord Howe Island. “Exsul” is an apt species name as it is Latin for “exile”, and its ancestor probably dispersed to Lord Howe all the way from New Zealand. 6 New Zealand Garden Journal, 2016, Vol. 19(1) Table 1 New Zealand native species of Carmichaelia. Botanical name Common name(s) Growth habit and distinguishing features Appressed broom, Prostrate (to decumbent) ground cover, *C. appressa G.Simpson prostrate broom white/purple flowers South Island broom, C. arborea Druce Shrub or small tree, scented white/purple flowers swamp broom, tree broom Dwarf and spreading ground cover, C. astonii G.Simpson Aston’s dwarf broom white/purple flowers *C. australis R.Br. Common native broom Shrub or small tree, white/purple flowers Shrub or small tree, slender drooping branchlets, †C. carmichaeliae (Hook.f.) Heenan Marlborough pink broom abundant pink flowers *C. compacta Petrie Cromwell broom Erect or spreading shrub, purple flowers *C. corrugata Colenso Common dwarf broom Dwarf and rhizomatous, purple flowers C. crassicaulis Hook.f. Robust shrub, grooved branches, Coral broom subsp. crassicaulis off-white / purple flowers *C. crassicaulis subsp. racemosa Spreading to upright shrub, grooved branches, Slender coral broom (Kirk) Heenan off-white / purple flowers Spreading to sprawling sparsely branched shrub, *C. curta Petrie Waitaki Broom, whip broom purple/white flowers Shrub or small tree, slender drooping branchlets, *†C. glabrescens (Petrie) Heenan Marlborough pink broom abundant pink flowers Low-growing shrub, *C. hollowayi G.Simpson Holloway’s broom, whaupaku purple or red purple / white flowers Prostrate and sprawling shrub, C. juncea Hook.f. (No common name known) flowers white with various shades of purple Climbing broom, Kirk’s Sprawling shrub or climbing vine, *C. kirkii Hook.f. broom, scrambling broom white/purple flowers Dwarf and spreading, †C. monroi Hook.f. Stout dwarf broom white and pinkish-purple flowers Clifford Bay broom, Small tree, upright growth habit, *C. muritai (A.W.Purdie) Heenan coastal tree broom white/purple-violet flowers Dwarf ground cover, purple *†C. nana (Hook.f.) Hook.f. Dwarf broom (or rare creamy-white) flowers Leafy broom, maukoro, *†C. odorata Benth. Leafy shrub, scented white/purple flowers scented broom C. petriei Kirk Desert broom Shrub, white/purple-violet flowers Cord broom, Small tree, weeping stems, *†C. stevensonii (Cheeseman) Heenan weeping tree broom abundant sprays of pale lavender flowers C. torulosa (Kirk) Heenan Canterbury pink broom Small tree or large shrub, pink/purple flowers Dwarf broom, Dwarf and rhizomatous ground cover, *C. uniflora Kirk single-flowered broom white/purple flowers C. vexillata Heenan Dwarf broom Dwarf and spreading, pinkish purple flowers Giant-flowered broom, Robust shrub, broad and flattened cladodes, *†C. williamsii Kirk William’s broom creamy-yellow flowers * = currently available from native plant nurseries. † = particularly recommended for cultivation. Low-growing brooms damage by off-road vehicles and There are nine species of low-growing, other disturbances. Following the prostrate, decumbent or dwarf native New Zealand Threat Classification brooms. Most are restricted to the System, it is classified as an “At Risk eastern South Island. Their low stature – Naturally Uncommon” species. and preference to grow in dry, open C. appressa has yellowy-green and sunny conditions makes them cladodes and white flowers streaked ideal for rock gardens, container plants, with purple. It is a prostrate shrub that or as ground covers on exposed sites. grows to 25–40 cm tall with a spread The tight growing dwarf species are of up to 2 m in the wild, although especially good in rock gardens. 0.5(–1) m across is more usual in cultivation. This species is ideally Carmichaelia appressa (appressed suited to rock gardens or retaining broom, prostrate broom): a species walls where there is good drainage. largely restricted to Kaitorete Spit near Christchurch, where it grows Carmichaelia astonii (Aston’s dwarf on stabilised sand dunes and ridges broom): a “Threatened – Nationally (Fig. 2). Although most plants Fig. 2 Carmichaelia appressa growing Vulnerable” species confined to a are protected within a scientific wild in the seemingly barren Kaitorete Spit few limestone cliff areas in eastern reserve, they remain vulnerable to landscape. Photo: Peter Heenan. Marlborough. This dwarf and spreading New Zealand Garden Journal, 2016, Vol. 19(1) 7 shrub grows to 20 cm tall (rarely to workmate who was gearing up to Carmichaelia nana (dwarf broom): 50 cm tall for old plants in cultivation) access this species by abseiling off an “At Risk – Declining” species found and up to 50 cm across. This species the main road bridge across Fox River. in scattered locations in the North has greenish-brown cladodes and When we showed up, the river was Island (Central Volcanic Plateau) and produces an abundance of white unusually low and we could reach the South Island (Marlborough, Canterbury flowers streaked with purple. It is easy plants wearing gumboots. At this site, and Otago). North Island plants were to grow and does best in well-drained C. juncea was growing on an island previously known as C. orbiculata and soil enriched with added lime in a sunny formed by forks in the river that usually South Island plants as C. enysii, but position. prevented herbivores (and humans) in 1995 my colleague Peter Heenan, from reaching the population of this as part of his PhD revisions of the Carmichaelia astonii is restricted to threatened broom. C. juncea has a native brooms, accepted a broader limestone in Marlborough and allied to sprawling, prostrate growth habit and circumscription, reducing both names C. monroi and C. vexillata. The three forms flattened mats up to 20 cm to synonyms of C. nana. This species native brooms that are restricted to tall and 1.5 m across. Flowers are is usually found in open places, river limestone habitats (called calcicoles) white or with various shades of purple terraces and moraines.