Lepidium peregrinum (Brassicaceae)—a new addition to the New Zealand flora

Abstract

Lepidium peregrinum (Brassicaceae) is recorded for the first time in New Zealand, where it was collected from O Wiwi Ku, an island in Kawhia Harbour, western North Island. Although native to eastern Australia, L. peregrinum was initially described from plants collected wild in the United Kingdom. This and other European occurrences are believed to have arisen from seed trapped within sheep fleeces imported from Australia. It is suggested that the sole New Zealand occurrence also results from the importing of goods directly from Sydney, New South Wales, to Kawhia by Maori during the 1830s to 1860s. A description of L. peregrinum based on New Zealand specimens is provided. The biostatus of L. peregrinum is reviewed and, despite being treated as naturalized, it is concluded that the species poses no threat to the indigenous New Zealand flora. As a threatened Australian plant, recommendations are made about the conservation management of the species in New Zealand.

Keywords:

• Brassicaceae
• Lepidium
• L. peregrinum
• L. africanum
• L. desvauxii
• L. hyssopifolium
• L. pseudohyssopifolium
• L. pseudotasmanicum
• biostatus
• trans-Tasman dispersal
• New Zealand flora

Introduction

During January 2010, on a brief visit to O Wiwi Ku, an island in Kawhia Harbour (38°5′28.34′′S, 174°52′00.03′′E) (Fig 1), one of us (PdL) collected from the southern side of the island a few leaves and a fruiting inflorescence of a rather tattered plant of an unknown Lepidium (P. J. de Lange 9225, AK 316005) found growing on a small coastal cliff face amongst Rytidosperma racemosum, Dichelachne crinita and Barbarea intermedia. From the limited material available it was apparent that the Lepidium did not represent any species recognized by Garnock-Jones (1988) or Webb et al. (1995). The nearest match for the gathering was the Australian endemic Lepidium pseudotasmanicum Thell., which is naturalized throughout much of New Zealand, often in coastal habitats and on offshore islands (Garnock-Jones 1988).

Figure 1  Distribution of Lepidium peregrinum in Australia and New Zealand showing key locations noted in the text. A, inset showing location of eastern Australia in relation to New Zealand and position of expanded maps B and C. B, Australian distribution of Lepidium peregrinum (from Scarlett 1999)—locations of historical (these dated by last known plant collection) and extant populations in South Queensland and along the border of Queensland and New South Wales given as filled triangles. C, North Island of New Zealand showing position of expanded map D. D, Western Waikato showing the three main western Waikato harbours, location of O Wiwi Ku island and other key areas discussed in text.

As the original collection was inadequate for a proper identification, seed from that gathering was sown and flowering and fruiting plants subsequently identified. In this paper, we report L. peregrinum Thell. as an addition to the naturalized New Zealand flora and review its biostatus, provide a description based on New Zealand material and compare it to other morphologically similar naturalized Lepidum species present in New Zealand with which it may be confused.

Taxonomy

Lepidium L.

Lepidium peregrinum Thell. in Druce, Botanical Exchange Club of the British Isles 3(3): 153, (1913), t.9.

Description (of New Zealand specimens only; Fig 2): Perennial herb to sub-shrub, up to 0.8 m tall. Stems erect to spreading, slightly angular and ridged, sparsely to moderately vestured on surface with short patent hairs. Rosette and lower cauline leaves 80–190 mm long, 12–40 mm wide, petiolate, lamina lyrate-pinnatifid to lyrate-pinnatisect, terminal lobe broad-lanceolate, usually vestured with long-acicular hairs on the upper surface and margins; lateral lobes with distal margins serrate, proximal margins entire. Mid-cauline leaves 30–80 mm long, 1–9 mm wide, petiolate, lyrate-pinnatifid to lanceolate, margins serrate to serrulate; bases auriculate to sagittate, especially on lanceolate leaves. Upper cauline leaves 10–20 mm long, 1–1.5 mm wide, sessile to subsessile, narrow-lanceolate to linear, margins serrate or entire, bases attenuate at the point of leaf insertion. Inflorescences corymbose, elongating to 200 mm when in fruit. Branch-terminal racemes often appearing lateral and leaf-opposed, overtopped by a subtending axillary flowering branch. Rachis glabrous to minutely puberulent towards the apex, slightly angular and ridged. Sepals 0.6–0.9 mm long, 0.4–0.5 mm wide, the adaxial sepal dorsally villous in the upper half, the abaxial sepal glabrous or with one or four hairs, the lateral pair of sepals always glabrous. Petals 0.5–0.8 mm long, 0.1–0.2 mm wide, linear, or absent. Stamens 2, median, 0.9–1.1 mm long. Pedicels 3–5 mm long at maturity, erecto-patent to sub-declinate and usually arcuate at fruiting, sub-terete with a slightly flattened puberulent adaxial surface. Silicules 2.0–3.5 mm long, 1.7–2.2 mm wide, ovate to elliptical, acutely emarginate with triangular wings forming a v-shaped notch. Styles c. 0.1 mm long, included in the notch. Valves green or purple, glabrous. Seeds 1.1–1.5 mm long, 0.6–0.8 mm wide, narrowly ovoid, wingless.

Figure 2  Lepidium peregrinum showing diagnostic characters. A, Rosette leaves. B, Cauline leaves. C, Auriculate cauline leaf bases. D, Petiole hairs. E, Rosette leaf margin vestiture. F, silicle and arcuate pedicel showing adaxial vestiture.

Representative specimens: South Auckland: Kawhia Harbour, O Wiwi Ku (Meurant Island), P. J. de Lange 9225, 13 January 2010, AK 316005.Cultivated: Oratia Native Plant Nursery, ex O Wiwi Ku, P. J. de Lange 9603 & G. R. Davidson, 8 February 2011, AK 321827; Landcare Research experimental nursery, ex O Wiwi Ku, P. B. Heenan s.n., 18 August 2010, CHR 605029; Landcare Research experimental nursery, ex O Wiwi Ku, P. B. Heenan s.n., 10 September 2010, CHR 605028; Landcare Research experimental nursery, ex O Wiwi Ku, P. B. Heenan s.n., 24 March 2011, CHR 605030.

Distribution and habitats: L. peregrinum is only known in New Zealand from O Wiwi Ku (known also as Meurant or Green Island), a small (c. 0.4 ha) mostly grass-covered island located on the southern side of the Kawhia Harbour, opposite the Rakaunui Peninsula (Fig 1). O Wiwi Ku is composed of indurated, fossiliferous, glauconitic limestone, which is believed to be a basal sequence within the Orahiri Limestone (Nelson 1978; Fergusson 1986; White & Waterhouse 2010; C.S. Nelson pers. comm.). The original vegetation of the island is highly modified (de Lange 1983), and possibly because the island is exposed and drought prone the island's flora has been almost completely dominated by grasses for at least the last 100 years (R and L Takiari pers. comm.). The dominant grasses noted during the January 2010 visit to the island were Rytidosperma racemosa, R. unarede, Microlaena stipoides and on the rock shore platform and cobble beaches Austrostipa stipoides. Along the north-western and southern sides of the island this grassland is broken by a few wind-shorn Myrsine australis and, on the south-eastern side there is a single ancient peach tree (Prunus persica).

In January 2010, L. peregrinum plants were observed at only one site, growing on a rendzina soil that has developed over the limestone and which is partially exposed along the small cliffs (1–3 m tall) that delineate the southern side of the island. Associated with the Lepidium were dried off plants of Barbarea intermedia and Rorippa divaricata, a threatened endemic cress (see de Lange et al. 2009; de Lange et al. 2010).

Subsequent searches of similar habitats along the southern side of the Kawhia Harbour during 2010 and early 2011 have failed to find further plants of L. peregrinum, though, as late-season more-or-less leafless fruiting plants are easily confused with L. pseudotasmanicum, which is very common in this area, it is possible that it has been overlooked.

Recognition: L. peregrinum is distinguished by a suite of characters, including the main stems and rachis being sparsely to moderately vestured with short patent hairs, the rosette and lower-cauline leaves being lyrate-pinnatifid to lyrate-pinnatisect (having a prominent terminal lobe), the mid-cauline leaves being lanceolate with serrate to serrulate margins and with distinctive auriculate bases, abaxially vestured pedicels that are arcuate at maturity and elliptical to ovate silicles that are shorter than the pedicels. New Zealand plants of L. peregrinum do not appear to differ from those of Australian populations.

L. peregrinum could be confused with L. pseudohyssopifolium Hewson, but the cauline leaves of this species have attenuate rather than auriculate bases and glabrous pedicels (very rarely with scattered hairs). L. pseudohyssopifolium is also very uncommon in New Zealand, being known only from a single gathering made in 1973 from Oamaru, South Island (Garnock-Jones 1988). L. peregrinum is also superficially similar to L. pseudotasmanicum. L. pseudotasmanicum differs from L. peregrinum by its usually glabrous stems and leaves; rosette and lower-cauline leaves pinnatisect to bipinnatifid and with the pinnae linear or narrow-oblong to oblong; mid-cauline leaves that are entire (oblanceolate to cuneate) or pinnatifid and with acute ± patent lobes; and often with only a single pair of lobes below the apex. Lepidium africanum, is another common naturalized species in New Zealand (Garnock-Jones 1988) that has a superficial similarity to L. peregrinum. In New Zealand there are two forms of L. africanum (see Garnock-Jones 1988) a glabrous form and a hairy form, both of which can be easily distinguished from L. peregrinum by the mostly simple rather than lyrate-pinnatifid rosette and lower cauline leaves, and by the attenuate rather than auriculate leaf bases of those leaves subtending branches. Other similar species are L. hyssopifolium Desv. and L. desvauxii Thell., but these are readily distinguished by the pedicels being hairy over the whole surface.

Biostatus: In its native country of Australia L. peregrinum is an uncommon and threatened species (Scarlett 1999; N.H. Scarlett pers. comm.). Prior to its discovery in New Zealand it had been recorded otherwise as a naturalized wool alien from the United Kingdom and Switzerland (Scarlett 1999). So we need to consider whether the New Zealand occurrence reported here is naturalized or indigenous. Given the remote New Zealand location for the species, it is perhaps more logical that it has dispersed naturally from Australia and should therefore be treated as indigenous to New Zealand (see de Lange & Rolfe 2010). Although this dispersal may have occurred recently, it could alternatively have been in New Zealand for a long time but have been overlooked and/or confused with the widespread, superficially similar and thoroughly naturalized L. pseudotasmanicum.

Indeed, NH Scarlett (in litt. 2006) suggested to PdL that L. peregrinum could be present in New Zealand, but overlooked because it is superficially similar to the naturalized L. pseudotasmanicum, L. pseudohyssopifolium, L. hyssopifolium and L. africanum (Burm.f.) DC. We have searched the main New Zealand herbaria (AK, CHR and WELT), and have not identified any other L. peregrinum specimens.

To infer an indigenous biostatus, a probable means of natural dispersal must be established (see comments by Heenan et al. 2009) or its presence before human arrival demonstrated. For the Australasian species of Lepidium it is known that their freshly dehisced seed is mucilaginous and therefore easily attached to the feathers and fur of passing animals (Norton et al. 1997; Thorsen et al. 2009). In this regard, the freshly dehisced seed of L. peregrinum has a mucilaginous surface, allowing it to readily attach to skin and clothing where it may remain for many hours (N.H. Scarlett pers. comm.). Furthermore, as L. peregrinum is now known from a few inland locations along the border between southern Queensland and northern New South Wales (Scarlett 1999) (Fig 1A & 1B), it is unlikely that seed reached New Zealand by any natural means other than by the movement of birds between both countries. However, the sole New Zealand occurrence of this species does not accord with any known historic or current roosting site or vagrant occurrence of trans-Tasman avifauna (C Miskelly & GA Taylor pers. comm.).

Therefore, we think it is more likely that L. peregrinum is naturalized in New Zealand, and that the most likely vector was the trade of livestock and goods between Sydney, New South Wales, Australia and Kawhia Maori (Figure 1A, 1C & 1D) during the 1830s to 1860s. The discovery and formal recognition of L. peregrinum in the United Kingdom provides support to this conclusion. Scarlett (1999) notes that the species was first described from material gathered from Galafoot near Galashiels, south of Edinburgh in the Scottish border country of the United Kingdom. It was deduced that these plants had temporarily established themselves from seeds washed out of imported Australian sheep fleeces into the Tweed River, as at that time whole fleeces were being routinely brought into that area for use in the tweed mills of Galashiels (Hayward & Druce 1919). Scarlett (1999) further notes that L. peregrinum was also found in Switzerland, where it was also treated as a “wool-alien”. It seems likely that L. peregrinum, although now scarce in its native country, was either once more widespread there, or growing in places where it was readily caught in sheep fleeces. As an acknowledged Northern Hemisphere wool-alien, it seems reasonable to infer the same status for the New Zealand occurrence.

Australian goods and livestock were being imported into the Kawhia area during the 1830s–60s, when local Maori were trading their wheat for such items directly from Sydney, Australia (see for example White 2009). At that time large parts of the Kawhia Harbour (Fig 1D) and immediate hinterland were given over to wheat cultivation, and numerous wharves and accommodation houses for merchants and travellers lined the harbour. Indeed, one such house and wharf was described from Te Aute Bay (Fig 1D), Rakaunui Peninsula, by the Austrian geologist Ferdinand von Hochstetter in 1859 (Fleming 1957), a location which lies less than 1 km from O Wiwi Ku. Based on this history, we consider it plausible that L. peregrinum was accidentally transported to Kawhia in goods or livestock derived from the hinterland of New South Wales, where it then became locally established. As regards its current scarcity, it is possible that L. peregrinum still occurs elsewhere in suitable habitats around the Kawhia Harbour but has been overlooked, that it failed to establish more widely, or that it was once more abundant but has undergone a decline and now persists only as a small population on O Wiwi Ku. In this regard, it is perhaps significant that the Northern Hemisphere occurrences were similarly short-lived and ultimately unsuccessful (Scarlett 1999).

The suggestion that L. peregrinum has naturalized from trans-Tasman trade, accords well with the postulated origin of wild Eremophila debilis (≡ Myoporum debile; Scrophulariaceae) occurrences in New Zealand. An Australian endemic species, E. debilis has been treated as indigenous to New Zealand by Allan (1961), but was known only from a few coastal locations south of the Raglan Harbour (Fig 1D) and at Te Maika, Kawhia (Fig 1D) (Wilson & Given 1989) where it persisted until 1980 (Chinnock 2007). It is now generally accepted that these occurrences stemmed from either the deliberate introduction and cultivation or temporary naturalization of the species in these areas from goods brought by traders from Sydney, Australia, to the Raglan and Kawhia harbours (see Webb et al. 1995; Chinnock (2007). Other examples of eastern Australian species that have naturalized in Central Otago, New Zealand, probably arriving as seed contaminants, but that failed to become well-established, include Convolvulus graminetinus, Australopyrum pectinatum and A. retrofractum (Connor et al. 1993; Heenan et al. 2003).

As we consider L. peregrinum to be naturalized to New Zealand we also need to consider its weed potential, in this country. Outside Australia, the only other known naturalized occurrences, those in the United Kingdom and Europe, are also now likely to be extinct (Scarlett 1999), suggesting that this species poses little risk to the flora of the countries in which it has or had established. This seems also to be the case for New Zealand. Certainly based on the behaviour of the species in the wild in New Zealand and our experience of it in cultivation in this country we suggest that it is not likely to be an invasive and troublesome weed.

Conservation status: The New Zealand Threat Classification System (Townsend et al. 2008, p. 25) makes provision for the recognition of taxa that are introduced and naturalized in New Zealand but which are listed as threatened in their country of origin by the IUCN. Currently, L. peregrinum has not been assessed by the IUCN (see IUCN Red List 2011), so on that basis the species is excluded from consideration by the New Zealand Threat Classification System (Townsend et al. 2008). Nevertheless, L. peregrinum has been listed as ‘Presumed Extinct’ (Briggs & Leigh 1995), and then as ‘Endangered’ by the Threatened Species and Communities, Biodiversity Group, Environment Australia (1998), which is also the status it has been given by the Department of Sustainability, Environment, Water, Population and Communities (2011). Globally, many species have failed to be assessed using the IUCN criteria, so as a formally listed Australian threatened endemic, we consider that some effort to collect and store seed of the New Zealand occurrence is justified.

Acknowledgements

The authors wish to thank Jeremy Rolfe for providing the map used for Fig 1. We also thank Neville Scarlett, David Norton and Phil Garnock-Jones for comments on a draft of this paper. Colin Miskelly and Graeme Taylor assisted us with information on trans-Tasman Australia to New Zealand bird movements, and records of vagrant species reported from the western Waikato. Cam Nelson updated PdL on the geology of O Wiwi Ku. We are deeply indebted to the oral history of Rakaunui recounted by the late Rohe Takiari of Rakaunui, Kawhia, to PdL during the 1980s, and which was augmented more recently by comments received from his surviving son, Lance Takiari.