Lepidium flexicaule Kirk, Trans. et Proc. New Zealand Inst. 14, 380 (1882)

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 : 36-45

Lepidium flexicaule Kirk, Trans. et Proc. New Zealand Inst. 14, 380 (1882)

Lectotype.

New Zealand (North Island) (fide Garnock-Jones and Norton 1995): Onehunga, n.d. T.Kirk 341 WELT SP030080! Isolectotypes: WELT SP030089!, WELT SP027620!

Etymology.

The exact meaning of the species ' flexicaule ' was not given by Kirk (1899) but the translation 'flexuous stems’ accurately characterises the plant.

= Lepidium incisum Banks et Sol. ex Hook.f., Flora Novae-Zelandiae 1, 15 (1853) nom. illeg., non Roth, Neue Beytr. Bot. 1: 224 (1802), nec Edgew., Trans. Linn. Soc. 20, 33 (1851)

Lectotype.

New Zealand (North Island) (fide Garnock-Jones and Norton 1995): Opuraga, on Beach, rare, n.d., Banks and Solander, BM! Isolectotypes: AK 100095!, WELT SP063696a, b!

Etymology.

Banks and Solander evidently chose the epithet ' incisum ' in allusion to the deeply incised leaves of their specimens.

Description

( Figs 38 -43 ). Tap-rooted, strongly pungent smelling, decumbent, summer-green, perennial herb forming densely leafy, patches up to 1.5 m diam., and arising from stout, semi-circular, whitish-grey (when exposed) rootstock 3-10 mm diam. when fresh. Tap root fleshy, yellow to yellow-white when fresh, up to 300 mm long, deeply descending. Plants dying down in winter or in times of adversity to rootstock (in well-grown individuals the new season’s branchlets may die back to the previous season’s stem nodes). Stems prostate, weakly flexuous, divergent to widely spreading, 100-800 mm long, 0.8-5.2 mm diam., woody near base, initially spherical in cross-section, pale yellow-green to dark green, sometimes tinged maroon and finely puberulent with short papillate or tapered hairs; becoming glabrous and prominently ridged and/or grooved with age, and usually bearing numerous leaf scars and withered petioles; upper portion of stems sparingly and openly to heavily branched; branches and branchlets, usually very leafy. Leaves glabrous, firmly fleshy to succulent, glossy dark green to yellow-green, at senescence turning yellow. Rosette and lower stem leaves withering at fruiting; petioles distinct 10-50 × 1-3 mm, slightly concave in cross-section, fleshy; leaves glabrous above, with papillae or denticles along midrib beneath and margins in New Zealand plants, or without denticles (absent in Chatham Islands and most Australian plants); lamina 50-90 × 15-30 mm, pinnatifid, obovate to oblanceolate; pinnae in 1-3 pairs, bluntly toothed or crenate at apex and distal margins. Upper stem leaves glabrous above, usually with triangular denticles, dense on margins and sparse to dense beneath (although absent in Chatham Islands and most Australian plants); mostly apetiolate, petiole if present minute up to 1.5 mm long; lamina 5-30 × 3-10 mm, obovate, oblanceolate, or spathulate, apex bluntly toothed to crenate, base broadly to narrowly cuneate. Racemes 10-50 mm long, elongating up to 60 mm at fruiting, terminal and leaf-opposed; rachis and pedicels puberulent with short tapering hairs, and ± covered in triangular denticles (absent in Chatham Islands and most Australian plants) or glabrous; axillary; rachis and pedicels hairs if present, retrorse to patent, very short, 0.05-0.8 mm long, ± clavate, eglandular - glandular; pedicels, erecto-patent to patent, initially 1.04-1.27(-2.38) mm; elongating to 2.34-5.00(-6.02) mm long at fruiting. Flower buds dark green, apex bearing a conspicuous, caducous, crest of white, eglandular, antrorse hairs up to 0.9 mm long. Flowers sweetly fragrant, 1.4-1.8(-2.3) mm diam. Sepals, broadly ovate to oval, apex broadly obtuse, centrally green with a white margin, deeply concave, adaxially weakly keeled, adaxial midrib invested in conspicuous, caducous, white, eglandular, antrorse, hispid hairs, hairs sometimes scattered across rest of adaxial surface; abaxial surface glabrous; lateral sepals broad, 0.6-1.0 × 0.6-1.2 mm, median sepals narrower 0.4-0.8 × 0.4-0.7 mm. Petals white, 0.3-0.8(-1.0) × 0.2-0.8 mm, erecto-patent or patent, clawed; limb broadly obovate, apex obtuse, retuse or distinctly emarginate. Stamens 2, equal. Anthers c.0.16 mm long. Pollen bright yellow. Nectaries 4, subulate, 0.40 mm long. Silicles cartilaginous when fresh, subcoriaceous when dry, (2.1-)3.3(-4.1) × (2.2-)3.3-3.4(-4.0) mm, orbicular, obovate, to ovate, slightly winged in upper ¼, apex scarcely or shallowly notched, valves green maturing yellow-green, glabrous; style 0.8 (-1.0) mm long, free from the narrow wing, equal to or slightly exceeding the notch; stigma 0.2-0.4 mm diam. Seeds 2, 1.20-1.38 × 0.80-1.10 mm, ovoid to suborbicular, red-brown, dark red-brown or brownish black, not winged. FL. Oct-Feb. FR. Dec-Apr.

Representative Specimens.

Australia (Tasmania): Port Davey, Gull Reef, January 1977, M. Allan s.n., (HO 26460); Port Davey, Elliot Point, 20 January 1986, A. Moscal 11876, (HO 402077); 1 km South of Rheuben Creek, 22 February 1985, A. Moscal 9734, (HO 401030); 1 km South of Nye Bay, 6 February 1986, A. M. Buchanan 8210, (HO 98828); Endeavour Bay, 30 January 1984, A. M. Moscal 6017, (HO 74481); Hibbs Bay, 25 January 1984, A. M. Buchanan 2775, (HO 74480); Bruny Island, n.d. L. Rodway s.n., (HO 54049). New Zealand (North Island): Great Barrier (Aotea island), Saddle Island, 7 January 1989, E. K. Cameron 5295, (AK 206897, AD, CHR).North Auckland, Waitemata, North Head, n.d., T. Kirk 342,(WELT SP030081); Waitemata, T. Kirk 41, n.d., WELT SP030088 (Duplicate AK 11429); Waitakere, May 1885, Ball s.n., (AK 261800); Bethell’s [Beach], 7 Jan 1934, L. M. Cranwell s.n., (AK 100102); Hauraki Gulf, Rangitoto Island, December 1882, T. F. Cheeseman s.n., (AK 4481); South Auckland, Manukau Harbour, Mangere, n.d., T. F.Cheeseman s.n., (AK 4480); Piako, n.d. J. Adams s.n., (AK 14865, AK 14866); Taranaki, Stent Road, 26 Jan 2010, P. J. de Lange 9279 & G. M. Crowcroft, (AK 317033), Kapiti Island, n.d. J. Buchanan s.n., (WELT SP087437). New Zealand (South Island): Between Little Whanganui River and Mokihinui, n.d.,?W. L. Townson 24, (WELT SP044035); Vicinity of Westport, 1903, W. Townson s.n., (WELT SP030082, WELT SP030084); Westport, Orowaiti River Bank, n.d., W. L. Townson s.n., (AK 253094); Westport, Orowaiti River Bank, 31 January 1953, R. Mason & N. T. Moar 2163, (AK 225200, CHR 81618); Cape Foulwind, n.d., W. Townson s.n., (WELT SP30085); Cape Foulwind, 4 February 1913, D. Petrie s.n., (WELT SP30086); Cape Foulwind, Tauranga Bay (Seal Colony), 14 August 1992, P. J. de Lange 1478 & D. A. Norton, (WELT SP079914); Punakaiki, 18 January 1931, L. B. Moore s.n. & L. M. Cranwell, (AK 100103). Chatham Islands: Rekohu, Point Somes, 25 January 2005, I. Keenan s.n., (AK 289897); Rekohu, Zimmermans Property, Point Somes, 10 January 2006, P. J. de Lange CH392, (AK 294940, CANB, CHR); Rekohu, Zimmermans Property, Point Somes, 10 January 2006, P. J. de Lange CH 395, (AK 294940, CANB, CHR, WAIK); Rekohu, Ocean Bay, Unnamed Point south west of Bay, 14 January 2006, P. J. de Lange CH440 & J. W. D. Sawyer, (AK 295121); Rekohu, Wharekauri Farm Station, Cape Young, 13 January 2006, P. J. de Lange CH425 & J. W. D. Sawyer, (AK 295154).

Distribution

( Fig. 44 ). Indigenous. Australia (Tasmania) and New Zealand (North, South, Chatham islands). In the North Island of New Zealand, Lepidium flexicaule is now known from only two extant populations, one on Saddle Island off the west coast of Great Barrier Island (Aotea Island) ( de Lange and Cameron 2011) and the other at Stent Road north of Cape Egmont, Taranaki ( Peet et al. 2003). Historically Lepidium flexicaule was present on Rangitoto Island, along the Waitakere Coastline, near North Head, Waitemata Harbour and near Onehunga, Manukau Harbour ( Kirk 1899; Cheeseman 1906, 1925; Garnock-Jones and Norton 1995). It was also recorded from the Firth of Thames, at Mercury Bay ( Kirk 1899; Cheeseman 1906, 1925; Garnock-Jones and Norton 1995) and near Wellington ( Garnock-Jones and Norton 1995). In the South Island, the species is confined to the western coast of North-West Nelson from near Kaihoka to about Point Elizabeth. Lepidium flexicaule was discovered on the northern portion of Rekohu in 2005 by Department of Conservation botanists.

Recognition.

Lepidium flexicaule is easily distinguished from all other indigenous Lepidium species by the combination of having a decumbent growth habit, pinnatifid rosette and basal stem leaves ( Figs 38 -41 ), and flowers with two stamens. Most North Island and South Island populations are further distinguished by the presence of tri angular denticles on branchlet stems, leaf margins and petioles, and on the rachis and pedicels of the inflorescences ( Fig. 42 , see also Garnock-Jones 1988). Denticles are, however, absent from the Chatham Islands, most Australian collections, and some South Island ones. The absence of denticles prompted the brief listing of Rekohu and Australian plants as an unnamed subspecies (see de Lange et al. 2009). However, as denticles are sometimes absent from South Island plants, formal taxonomic distinction may not be warranted. Nevertheless, it is worth noting that Rekohu plants are consistently larger than those seen from the rest of this species’ range, with well-grown specimens reaching up to 1.5 m diam., and that cpDNA data separates Tasmanian and Rekohu Lepidium flexicaule from New Zealand samples ( Fig. 4 ). Further study, including obtaining sequences of non-denticulate South Island Lepidium flexicaule , is warranted. Of the indigenous species, it is perhaps most similar to Lepidium naufragorum , which differs by its upright bushy shrub-forming habit with ascending to erect stems ( Fig. 55 ), more sharply serrated pinnae of the leaves; racemes that are not so clearly leaf-opposed and are much longer (up to 150 mm, cf. 50 mm long), flowers that have four rather than two stamens, and emarginate petals that are longer than the sepals (see Garnock-Jones and Norton (1995) for other distinctions).

Lepidium flexicaule is however, commonly confused in the field with the naturalised Lepidium didymum L. and Lepidium coronopus (L.) Al-Shehbaz, species with which it sometimes grows. Both Lepidium didymum and Lepidium coronopus have long been treated in New Zealand under the segregate genus Coronopus but Al-Shehbaz et al. (2002) reinstated both species within Lepidium . Lepidium flexicaule can be distinguished from Lepidium didymum and Lepidium coronopus by the valves of the silicles, which are smooth and which dehisce into 2 valves to leave a persistent replum. The silicles of Lepidium didymum and Lepidium coronopus have a reticulate-ridged or warty surface, and do not dehisce along the valves; in Lepidium didymum they split into 1-seeded segments and in Lepidium coronopus they are indehiscent.

Ecology.

The ecology of Lepidium flexicaule was described in some detail by Garnock-Jones and Norton (1995). They concluded that it is a strictly coastal species of turf communities, rock crevices and the strandline of bouldery beaches. Lepidium flexicaule has also colonised tracksides, the compacted peaty ground of seal colonies, bird roosts, and even bird nests, where plants presumably arose from fruiting material that had been used for nest construction. In most locations, the species is found within the spray zone and always in sites prone to frequent disturbance.

Conservation Status.

Previously Lepidium flexicaule had been assessed 'Threatened / Nationally Vulnerable CD, EF’ ( de Lange et al. 2009). Based on current evidence, this ranking is no longer appropriate, as Rekohu populations of this species (treated in that paper as an unnamed entity Lepidium aff. flexicaule but now included in Lepidium flexicaule (see recognition above)) and all of the monitored New Zealand Lepidium flexicaule populations are in decline, while the past total area of occupancy had been grossly under estimated. Based on current knowledge, Lepidium flexicaule is more appropriately assessed as 'Threatened / Nationally Endangered’ (criterion A(3/1) of Townsend et al. (2008)) because the total area of occupancy of the sum of the populations is <10 ha, and evidence obtained from monitoring indicates that there is an ongoing decline predicted to be up to 50% over the next ten years due to increased plant mortality (causes of which are as yet unknown) and loss of habitat caused by competition from weeds and coastal erosion. To this assessment we append the qualifiers ‘CD’ (Conservation Dependent - because virtually all known populations are being managed), ‘EF’ (Extreme Fluctuation - because monitoring also indicates that this is a species that, despite the decline, is naturally prone to seasonal population fluctuations) and ‘TO’ (Threatened Overseas - because, for the time being, we include Rekohu and Tasmanian plants within Lepidium flexicaule (see recognition), and in Tasmania Lepidium flexicaule is also seriously threatened (A. Buchanan pers. comm.)).

Hybridism.

On the Chatham Islands, Lepidium flexicaule is occasionally found growing with Lepidium oligodontum and Lepidium rekohuense , and putative hybrids have been collected when these species occur together. There is good evidence for the hybrid Lepidium flexicaule × Lepidium oligodontum (represented by AK 294939, P. J. de Lange CH391; AK 294942, P. J. de Lange CH394; AK 295119, P. J. de Lange CH442 & J. W. D. Sawyer). This hybrid is known from two sites on Chatham (Rekohu) Island where it is found in association with both parents. Like the parents, the hybrids have a decumbent growth habit. They share with Lepidium flexicaule pinnatifid rosette leaves, but vegetative features of Lepidium oligodontum are evident in the mid to upper stem leaves that are mostly spathulate to cuneiform (but with occasional deeply lobed margins to weakly pinnatifid leaves that are similar to Lepidium flexicaule ). The flowers of the hybrids have variable stamen numbers ranging from 1-5 per flower, compared to 2 in Lepidium flexicaule and 2-4-6 in Lepidium oligodontum , while pollen stainability varied from 80 to 85%. Seedlings raised from AK 295119 presented a bewildering array of foliage types grading into either parent. Unfortunately, through mishap these plants failed to reach maturity, so vouchers showing this are unavailable.

Evidence for Lepidium flexicaule × Lepidium rekohuense is less convincing. This putative hybrid is known from only one gathering (AK 295155, P. J. de Lange CH426 & J. W. D. Sawyer) which was collected in January 2006 from Cape Young, Rekohu, at a site where both parents grew. In the field, this specimen resembled Lepidium flexicaule closely except that the plant was distinctly leafy and the upper stem foliage was more copious and larger than is usual for Lepidium flexicaule . As with all Rekohu gatherings of Lepidium flexicaule , this specimen lacked stem and marginal leaf denticles. Furthermore, as with both parents, there are two stamens per flower, and pollen stainability of this gathering was 98%. No fruiting material was present, and on a subsequent search of this site in 2007 the putative hybrid and its parents had gone. This specimen may be a very well grown example of Lepidium flexicaule but, as it appears anomalous alongside other Rekohu, New Zealand, and Australian gatherings of that species, we prefer to treat it as a putative Lepidium flexicaule × Lepidium rekohuense hybrid.

The putative hybrid Lepidium flexicaule × Lepidium oleraceum has also been recorded once, as a spontaneous plant arising in cultivation at the Auckland Regional Council Botanic Gardens (AK 228296 S. P. Benham s.n., AK 223492 S. P. Benham s.n.). The hybrid grew in a site where both parents (Scots Beach Lepidium flexicaule and Stephens Island Lepidium oleraceum ) were planted together. The hybrid appeared from a seed lot gathered from the cultivated Lepidium flexicaule plant. It initially appeared to be different because it was much larger and more vigorous than Lepidium flexicaule , which it otherwise closely resembled (S. P. Benham pers. comm.). Over time, the hybrid developed weakly ascendant branches with rhomboid deeply serrated to pinnatifid mid and upper stem leaves, and flowers with 1-6 stamens. The hybrid appeared to be fully fertile, and seedlings raised from it showed clear segregation back to either parent (S. P. Benham pers. comm.). Again through mishap, these plants were lost before they reached maturity and specimens could be taken.

Figures

Figure 4. Maximum likelihood phylogeny of trn L-F as calculated in RaXML, showing the Lepidium oleraceum (black text) and Lepidium sisymbrioides (red text) groups, including the newly described taxa. Bootstrap support from 1000 replicates is shown for branches where it is greater than 50. Codes for each individual in the phylogeny are shown in Table 1.

Figure 38. Wild plant of Lepidium flexicaule growing on cobble beach showing decumbent growth habit (image: C. C. Ogle).

Figure 41. Old and new inflorescences of Lepidium flexicaule.

Figure 42. Close up of stems, upper-stem leaves and inflorescences showing denticles of Lepidium flexicaule. Scale bar = 5 mm.

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

Figure 55. Mature plant of Lepidium naufragorum on Taumaka Island (image: P. I. Knightbridge)