Lepidium limenophylax, Lange & Heenan & Houliston & Rolfe & Mitchell, 2013

Lange, P. J. de, Heenan, P. B., Houliston, G. J., Rolfe, J. R. & Mitchell, A. D., 2013, New Lepidium (Brassicaceae) from New Zealand, PhytoKeys 24, pp. 1-147 : 49-55

Lepidium limenophylax sp. nov.

A L. oleraceo G.Forst. habitu constanter decumbenti vel procumbenti, nodis caulorum ligneis repullantibus tempo novo et interdum radicibus adventiis, foliis constanter angusto-lanceolatis vel linearibus serrulatis floribus staminibus duobus, et DNA sequentiis singularibus differt.

Holotype.

New Zealand ( Fig. 50 ): Snares Island, Snares Island Expedition 1969/72, University of Canterbury, December 1969, C. H. Hay s.n., WELT SP077578!

Etymology.

The specific epithet ' limenophylax ' derives from Greek (Ό λιμνοφυλαξ) and, though it strictly means 'lake watcher’ (C. Blackford pers. comm.), it is used here in the sense of the alternative meaning of "harbour watcher or coast-guard", which Green (1994; p. 535) states is the more appropriate derivation (see his comments on the etymology of the Norfolk Island endemic orchid Phreatia limenophylax (Endl.) Benth.). It is given in allusion to the preferred habitat of Lepidium limenophylax on the Snares, i.e. the low turf confined to the exposed ends of rocky headlands jutting out into and overlooking the sea. Historically, it was on these exposed headlands that the World War II coastwatchers were posted to keep watch for signs of enemy shipping ( Fleming 1948, McEwen 2005).

Description

( Figs 51 -54 ). Tap-rooted, strongly pungent smelling, summer-green, perennial herb, arising from stout rootstock 7.3-10.0 mm diam. Plants dying down to rootstock and previous season’s stem nodes during winter. Stems decumbent, bases often very stout, ± spherical, somewhat woody when mature 10-15 × 10-12 mm, composed of numerous old leaf and stem bases, sometimes producing roots, new season’s grow decumbent, spreading 10-300 × 3-10 mm, glabrous, sometimes with very sparse, appressed, caducous, silky 0.5-1.0 mm long, hairs near stem apices, at fruiting, often devoid of foliage from much of length. Leaves glabrous, firmly fleshy to succulent, usually dark green to green, sometimes yellow-green. Rosette and stem leaves usually withering at fruiting but sometimes with a few long persistent. Petiole distinct, 20-40 × 2-4 mm lamina 50-100 × 5-15 mm, lanceolate, narrowly lanceolate to linear lanceolate; distal ⅓-⅔ finely but sharply serrated or crenate, teeth in 10-20 pairs running to and including subacute, obtuse to rounded apex (teeth not extending beyond leaf outline), base cuneate to narrowly cuneate. Middle stems leaves with petiole indistinct, lamina narrowly linear lanceolate to linear, often recurved to falcate in the distal ⅓ - ½ of leaf length, 50-120 × 3-6 mm; upper ⅔ or occasionally the entire leaf finely but sharply serrated; teeth in 12-30 pairs running to and including the apex, and not extending beyond leaf outline, lamina base tapered, very narrowly cuneate. Upper stem leaves with or without a distinct petiole, petiole if present 40-60 mm, linear to linear-spathulate, occasionally narrowly lanceolate, often recurved or falcate from ½ of leaf length, 30-100 × 2.0-30.0 mm, margins finely but sharply serrated. Racemes 5-15 mm long, terminal and axillary; rachis glabrous; pedicels glabrous, erecto-patent, 2-8 mm long at fruiting. Flowers c. 0.4-1.0 mm diam. Sepals 4, saccate, overlapping at base, green with pale-green to white thickened margin, apex broadly obtuse, shape and size dimorphic; lateral sepals c.0.6-1.0 × 0.6-1.2 mm, broadly ovate to oval, mostly glabrous, sometimes sparsely hairy, hairs 0.2-0.4 mm long, caducous; median sepals 0.9-1.2 × 0.5-1.2 mm, elliptic to obovate, abaxial surface sparsely hairy, hairs 0.2-0.4 mm long, caducous. Petals white to off-white, 1.5-2.0 × 0.3-1 mm, erecto-patent to somewhat spreading, clawed; limb narrowly obovate, apex obtuse, occasionally emarginated. Stamens 2, equal. Nectaries 2, subulate, 0.35 mm long. Silicles cartilaginous when fresh, coriaceous when dry, 2.5-3.5 × 1.5-3.3 mm, elliptic or rhomboid, not winged, apex usually notched (rarely truncate), valves green maturing yellow-green, glabrous; style 0.1-0.3 mm long, exceeding the shallow notch (if notch present); stig ma 0.3-0.5 mm diam. Seeds 2, narrowly ovoid, brown, red-brown to orange-brown, not winged, 1.25-1.3 × 0.35-0.60 mm. FL. Nov-Feb. FR. Nov-Feb.

Representative Specimens.

New Zealand (Stewart Island/Rakiura): Kaimohu Island, 25 February 1965, B. A. Fineran s.n., (CANU 8703). Snares Islands: No vember 1907, B.C. Aston s.n., (AK 4464, WELT SP027621, WELT SP027628); January 1909, B. C. Aston s.n., (WELT SP027623, WELT SP027624, WELT 27625, WELT SP027626); west coast between Signpost Hill and Razor Back, 29 November 1984, G. S. Hardy s.n., (WELT SP078810); on headland just below Signpost Hill, 29 November 1984, G. S. Hardy s.n., (WELT SP078811); December 1947, n. c., R. C. Murphy Expedition, (WELT SP035432); December 1947, F. Newcombe s.n., (WELT SP09710); cliff edge, February 1961, B. Fineran s.n., (CANU 5949); cliff edge, February 1961, B. A. Fineran s.n., (CANU 5950); B. Fineran s.n., Feb 1961, cliff edge, CANU 5994; cliff edge, February 1961, B. A. Fineran s.n., (CANU 5995); cliff edge, February 1961, B. A. Fineran s.n., (CANU 6000A-6000B); Broughton Island, 4. November 1972, D. S Horning s.n., (CANU 18916); July 2002, P. Sagars.n., (AK 283482). Auckland Islands: January 1890, T. Kirk s.n., (WELT SP027634).

Distribution

( Fig. 44 ). Endemic. New Zealand, South-western Titi (Muttonbird) Islands (Kaimohu Island), The Snares (North East, Broughton islands), and Auckland Islands. Lepidium limenophylax is possibly also present on Pohowaitai Island (B. A. Fineran, 4 Mar 1965, CANU 8723) another of the south-western Titi (Muttonbird) Islands, although this collection, comprising sterile specimens of a whole young plant and a branch are inadequate to be certain. There are also additional unconfirmed observations of what may be this species from many of the other south-western Titi (Muttonbird) Islands (B.A. Fineran and B.D. Rance pers. comm.).

Recognition.

Lepidium limenophylax is recognised by the decumbent growth habit ( Figs 51 , 52 ), with plants developing a distinct woody network of branches. New season’s growth arises from the nodes left from the previous season’s growth. In this species, the leaves are consistently lanceolate, narrowly lanceolate, linear lanceolate or linear ( Figs 50 , 51B , 52 ), though slightly broader in seedlings and basal rosettes. The flowers have two stamens ( Fig. 53 ). It is morphologically most similar to Lepidium rekohuense , which also has a decumbent growth habit and flowers with two stamens. Lepidium limenophylax has lanceolate, narrowly lanceolate, linear lanceolate or linear leaves, rather than the spathulate to narrowly ovate or elliptic leaves of Lepidium rekohuense . Furthermore, the silicles of Lepidium limenophylax are elliptic, rhomboidal and unwinged ( Fig. 54 ), rather than orbicular, obovate to ovoid and winged.

Ecology.

On the Snares, Lepidium limenophylax has been described as an occasional component of cliff top vegetation where it is stated to grow in association with living or dead Poa astonii Petrie pedestals (and on occasion in association with Poa tennantiana Petrie and Hebe elliptica (G.Forst.) Pennell), often near the feeding sites of brown skuas ( Stercorarius lonnbergi Mathews, 1912) and occasionally around the nests of Buller’s mollymawk ( Thalassarche bulleri (Rothschild, 1893)) or on dry peaty cliff tops (sometimes within the sandy quartz derived from the underlying granite) ( Fineran 1969, Hay et al. 2004, Lake and Evans 2011). Further inland, it was also reported by Fineran (1969, p. 3) 'as uncommon... sometimes present on sites of old abandoned penguin rockeries, where it usually grew with great vigour’. Brian Rance (in litt.), on a visit to the islands in 2000, found that, as with Fineran (1969), Lepidium limenophylax was virtually confined to the north-western cliffs. More recently, Lake and Evans (2011) failed to find it at any inland sites. All these authors and individuals noted Lepidium limenophylax as uncommon in other habitats, though a few plants have been noted near Boat Harbour growing in association with Poa astonii , Asplenium obtusatum G.Forst.and Hebe elliptica in semi-open situations caused by Hooker’s sea lions ( Phocarctos hookeri (Gray, 1844)) ( Lake and Evans 2011; B. D. Rance pers. comm.). Very little is known about the associations of Lepidium limenophylax on Kaimohu Island, though herbarium notes suggest that it grew there in association with what is probably Lepidium juvencum (see comments under that species), and B. A. Fineran (pers. comm.) noted that this species was present mostly along ridge crests and above cliff faces, always in association with the feeding sites of skua. Brian Rance (in litt.) has also observed plants apparently matching Lepidium limenophylax on several of the Titi (Muttonbird) islands south west of Stewart Island, usually growing along tracks in association with a sparse ground cover of Apium prostratum subsp. prostratum var. filiforme (A.Rich.) Kirk, Nertera depressa Banks et Sol. ex Gaertn and Poa astonii under semi-open Olearia angustifolia Hook.f. / Olearia lyallii Hook.f. short forest.

Conservation Status.

On the Snares Lepidium limenophylax occupies a very narrow habitat range scattered over four key areas and covering an area of 943 m2 ( Lake and Evans 2011). Lake and Evans (2011) were unable to count or estimate population size stating that 'it was not possible to estimate the number of plants due to the tendency [of the species] to grow in patches and not [as] isolated plants’. Nevertheless, they reported 'a good mix of mature and juvenile plants’. Outside these islands, the status of this species on the Auckland and south-western Titi (Muttonbird) Islands is unknown. Previously, Lepidium limenophylax , as Lepidium aff. oleraceum (c) (CANU 5995; Snares), had been listed by de Lange et al. (2009, p. 89) under Appendix 2 Taxonomically Indeterminate Listings, as 'Acutely Threatened/Nationally Critical’ with the qualifiers ‘IE’ (Island Endemic) and ‘RR’ (Range Restricted) appended. That assessment used data provided by B. D. Rance, on a visit to the Snares Islands in 2000. Lake and Evans (2011) provided a detailed update on the information obtained by Rance during a three week stay on the Snares between September and October 2010. They concluded that the species was in good health, and much more abundant than had been believed previously. While these observations suggest that this is probably a narrow-range species secure within its Snares stronghold, we recommend retention of the current threat listing of de Lange et al. (2009) as a precautionary measure because: 1. Accurate information about the status of this species outside the Snares is absent (i.e. it is not a Snares endemic), 2. The total area of occupancy on the Snares is <1 ha (criterion A(3) in Townsend et al. (2008)) and 3. There is still no trend data available for the species. However, to reflect the observations of Lake and Evans (2011) and our ongoing uncertainty about population trend and the status of this species outside the Snares we recommend that the addition of the qualifier ‘DP’ (Data Poor) to the current threat listing. It should also be noted that because Lepidium limenophylax is known from a number of islands and island groups it does not meet the definition of ‘IE’ in Townsend et al. (2008). Lepidium limenophylax also should be qualified ‘CD’ (Conservation Dependent) because the largest known population occurs within a Nature Reserve and World Heritage site (The Snares) where it is vulnerable to the spread of disease, weed and rat incursions, all of which would have a profound impact on its long-term security. Because of these threats, which put at risk not only the Lepidium but all other Snares terrestrial biota, access to the islands is strictly controlled by the New Zealand Department of Conservation, which also undertakes regular biosecurity inspections of the island group.

Figures

Figure 44. Distribution of Lepidium flexicaule (New Zealand distribution shown only), Lepidium juvencum, Lepidium limenophylax, Lepidium naufragorum and Lepidium obtusatum.

Figure 50. Holotype of Lepidium limenophylax de Lange, B. D. Rance et D. A. Norton.

Figure 51. Lepidium limenophylax: (A) flowering plants on the Snares in Poa astonii / Poa tennantiana grassland showing decumbent growth-habit (image: R. Ewans); (B) close up of young and emergent inflorescence (image: S. Lake).

Figure 52. Lepidium limenophylax: (A) broad-leaved leaf variant (rosette leaves) (image: R. Ewans); (B) narrow-leaved variant (image: R. Ewans).

Figure 53. Inflorescence of Lepidium limenophylax showing flowers and stamens (image: R. Ewans).

Figure 54. Mature silicle of Lepidium limenophylax. WELT SP 077578. Scale bar = 1 mm.