Lepidium oleraceum
Common name
Nau, Cooks scurvy grass
Synonyms
Lepidium oleraceum var. acutidentatum Kirk, L. oleraceum var. frondosum Kirk, L. oleraceum var. serrulatum Thell.
Family
Brassicaceae
Flora category
Vascular – Native
Endemic taxon
Yes
Endemic genus
No
Endemic family
No
Structural class
Dicotyledonous Herbs other than Composites
NVS code
The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.
LEPOLE
Chromosome number
2n = c.72
Current conservation status
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2017 using the New Zealand Threat Classification System (NZTCS). This report includes a statistical summary and brief notes on changes since 2012 and replaces all previous NZTCS lists for vascular plants. Authors: By Peter J. de Lange, Jeremy R. Rolfe, John W. Barkla, Shannel P. Courtney, Paul D. Champion, Leon R. Perrie, Sarah M. Beadel, Kerry A. Ford, Ilse Breitwieser, Ines Schönberger, Rowan Hindmarsh-Walls, Peter B. Heenan and Kate Ladley.
2012 | Threatened – Nationally Endangered | Qualifiers: CD, DP, EF, RR, Sp
Previous conservation statuses
2009 | Threatened – Nationally Vulnerable | Qualifiers: CD, EF, RR, Sp
2004 | Threatened – Nationally Endangered
Distribution
Endemic. New Zealand, Kermadec Island group, Three Kings Island group, North, South, Stewart Islands and the Bounty Islands group.
Habitat
Now strictly coastal, L. oleraceum is usually found in friable well manured soils, guano deposits, or rock crevices associated with seabird roosts and nesting sites. Occasionally it grows under taller vegetation, and then usually near petrel or shear water burrows. The species is now mainly found on rock stacks, islets, and windshorn headlands on rodent free offshore islands. In some places it has been found growing on sand or gravel beaches, and in one location it grows on boulders and clay that are part of an artificial sea wall. Historically this species was also known from the upper Waitaki Valley, well inland from the sea. This suggests that before human occupation it was once more widespread away from coastal situations.
Features
Glabrous, much-branched, perennial, herb up to 1 x 1 m, usually less. All parts strongly pungent when bruised. Stems erect to decumbent, stout, somewhat woody near base, flexuous. Petioles winged of variable length. Leaves 20-100 x 15-40 mm, decreasing in size toward stem apices, dark green to green, fleshy, somewhat succulent, narrow-oblanceolate, obovate to elliptic, margins, deeply and evenly serrated, cuneately narrowed at base. Inflorescences racemose, terminal and lateral, usually leaf-opposed 30-150 mm at fruiting; pedicels erecto-patent, 3-10 mm long at fruiting. Flowers fragrant. Sepals 1-2 x 0.5-1 mm. Petals white, 2.5-3.5 x 0.5-2 mm, obovate-spathulate. Stamens 4, yellow. Silicles 3-5 x 2.5-5 mm, broadly ovate, truncate at base, apex acute, not winged; style 0.1-0.2 mm; seeds 1.5-2 mm, ovoid, orange-brown
Similar taxa
Distinguished from all other indigenous and exotic Lepidium species by the glabrous stems, persistent, toothed, stem leaves, glabrous pedicels, flowers with four stamens and by the acute silicles which lack a marginal wing.
Flowering
Flowers appear year-round, but mainly from September to March.
Flower colours
White, Yellow
Fruiting
Fruiting occurs from December to April. Seed production is rapid so flowers, immature and ripe seed capsules are often found on the same plant.
Life cycle
Mucilaginous seeds are dispersed by attachment and possibly wind and water (Thorsen et al., 2009).
Propagation technique
Easy from fresh seed. Can be grown from semi-hardwood cuttings. Fast growing. Does best in friable soils enriched with N, P, K, in full sun. This species, and indeed all other representatives of the genus in New Zealand are very prone to fungal diseases and insect attack, and can be difficult to maintain. Lepidium oleraceum is best treated as an annual.
Threats
Seriously threatened by loss of indigenous sea bird nesting grounds because it is dependent on high-fertility soils and regular cycles of animal induced disturbance. It is susceptible to a range of introduced pests and diseases, including rodents, snails, aphids, leaf miner, diamond back moth and cabbage white butterfly, and is browsed by cattle and other livestock. A fungus-like disease (Albugo candida (J.F.Gmel.) Kuntze) is also a problem; and the plant has been and continues to be over-collected by people.
Etymology
lepidium: Scale-shaped (pods)
oleraceum: As a vegetable
Taxanomic notes
Chatham, Antipodes, Snares and Auckland Island plants differ from L. oleraceum s.s. Their taxonomic status is under review. Cooks scurvy grass or nau, played a vital role in preventing scurvy in ship crews visiting New Zealand during the late 1700s and early 1800s. All parts of the plant are edible. The Maori name nau is of ancient derivation and is found in varying forms throughout Polynesia. Many Pacific Island peoples have traditions of harvesting and/or cultivating related lepidia as a vegetable food and suggests NZ Maori may well have used L. oleraceum and allied species in the same way.
Attribution
Description adapted from Webb et al. (1988).
References and further reading
Allan, H.H. 1961. Flora of New Zealand. Volume I. Indigenous Tracheophyta: Psilopsida, Lycopsida, Filicopsida, Gymnospermae, Dicotyledones.Wellington, Government Printer.
Thorsen, M. J.; Dickinson, K. J. M.; Seddon, P. J. 2009. Seed dispersal systems in the New Zealand flora. Perspectives in Plant Ecology, Evolution and Systematics 11: 285-309
Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. 1988. Flora of New Zealand. Volume IV. Naturalised Pteridophytes, Gymnosperms, Dicotyledons.Christchurch, New Zealand, Botany Division, D.S.I.R.