Lepidium juvencum, 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 : 45-49

Lepidium juvencum sp. nov.

A L. oleraceo habitu decumbente vel effuso patuloque, caulibus sparsis effusis gracilibus flexilibus, foliis subcoriaceis, apice obtuso vel truncato, plerumque 2--3 dentibus prominentibus ut videtur irregularibus, floribus fructibusque e plantis juvenibus prodientibus, et propria sequentia nucleotidorum DNA distinguenda.

Holotype.

New Zealand ( Fig. 45 ): Otago Land District, Otago Peninsula, Long Beach, Purakanui, on stabilised sand at base of cliff amongst introdued grasses, 26 November 2009, P. B. Heenan s.n., CHR 609785B! Isotype CHR 609785A!

Etymology.

The specific epithet ' juvencum ' from the Latin for ' youthful ' refers to plants flowering and fruiting only a few months after germinating from seed.

Description

( Figs 46 -49 ). Tap-rooted, strongly pungent smelling, perennial herb. Growth habit open, straggly, up to 50 cm tall. Stems usually decumbent to sprawling, slender, flexible, sparse; mature stems woody, 100-1000 × 8-12 mm, often devoid of foliage on middle and lower parts of stems; new stems 100-400 × 3-4 mm, leafy, glabrous. Leaves glabrous, subcoriaceous, green, often undulate, rosette and stem leaves usually withering, variable in size and shape. Leaves of young and vigorous plants and stems: lamina 37-87 × 12-32 mm, elliptic, obovate or elliptic-oblanceolate; apex truncate to obtuse, usually with 2-3 prominent teeth and often appearing irregular; margin singly crenate, with 4-19 pairs of teeth; teeth up to 1.5 mm deep, not overlapping; base attenuate to cuneate, tapering to a distinct or indistinct petiole; petiole up to 23.0 × 2.0-5.0 mm, or sessile. Leaves of mature plants and cauline stems: lamina 10-60 × 3-21 mm, elliptic, elliptic-oblanceolate, obovate to elliptic-obovate; apex subacute, truncate or obtuse, usually with 2-3 prominent teeth and often appearing irregular; margin singly crenate in upper and/or lower half, with 4-19 pairs of teeth; teeth up to 1.3 mm deep, not overlapping; base attenuate to cuneate, tapering to distinct or indistinct petiole, or sessile. Inflorescence terminal and lateral, racemose, 10-60 mm long, rachis 1.0-1.3 mm diam., glabrous; pedicels 4.0-6.0 mm long, erecto-patent, usually glabrous although lower pedicels occasionally sparsely hairy on adaxial surface. Flowers 4.0-5.0 mm diam. Sepals 4, 1.3-1.5 mm long, saccate, overlapping at base, green, apex obtuse, margin white, shape dimorphic; lateral sepals broad, 1.1-1.5 mm diam., orbicular, abaxial surface often hairy, hairs 0.1-0.5 mm long; median sepals narrow, 0.9-1.2 mm diam., broadly elliptic, glabrous. Petals white, 2.0-2.4 × 1.1-1.5 mm, spreading, claw 0.6-1.0 mm long; limb broadly elliptic to orbicular, apex obtuse to rounded. Stamens 4(-5); filaments 1.4-1.7 mm long, base 0.3-0.5 mm diam., equal; anthers 0.3-0.4 mm long. Ovary 1.0-1.5 × 0.9-1.4 mm, broadly ovate to broadly elliptic, green to green-brown, apex usually with shoulders; style 0.15-0.25 mm long, cylindrical; stigma 0.3-0.5 mm diam. Nectaries 4, 0.2-0.3 × c. 0.1 mm, oblong-obovate, green. Silicles cartilaginous when fresh, coriaceous when dry, 3.1-4.2 × 2.5-3.5 mm, elliptic-rhomboid to orbicular-rhomboid, valves light brown,glabrous, apex shallowly notched, not winged; style 0.2-0.3 mm long, exserted. Seeds 1.6-1.8 × 0.9-1.3 mm, narrowly ovoid, brown to orange-brown, not winged. FL Nov-May. FR Nov-Jun.

Representative Specimens.

New Zealand (South Island): Otago, Long Beach, 30 December 1998, G. S. Stone s.n., (AK 239841); Otago, Long Beach, 25 Jun 1997, D. Nelson s.n. & J. Barkla, (CHR 518601); Otago, Long Beach, 13 July 2009, P. B. Heen an s.n., (CHR 609779);Otago,Long Beach, 14 July 2009, P. B. Heenan s.n., (CHR 609780); Tomahawk Beach, 4 February [1920?], B. C. Aston s.n., (WELT SP027651, WELT SP052362); Tavora Reserve, 13 July 2009, P. B. Heenan s.n., (CHR 609786-609789);Otago Peninsula,Green Island, January 1955, R. A.. Falla s.n., (WELT SP038744); Otago Peninsula, Green Island, January 1957, M. E. Gillham s.n., (CHR 111452); Otago Peninsula, Green Island, 6 July 1983, P. N. Johnson 70, (CHR 404351); Otago Peninsula, Green Island, 27 March 1989, P. N. Johnson 823, (AK 185642, CHR 461272); Otago Peninsula, Green Island, 12 February 1999, G. Loh s.n., (AK 238646); Solander Island, 10 November 1973, P. N. Johnson s.n., (CHR 253066). New Zealand (Stewart Island/Rakiura): Halfmoon Bay, Mill Bay, 4 February 1963, P. Hynes s.n., (AK 92212); Womans Island, January 1976, P. N. Johnson s.n., (CHR 261892); Herekopare Island, 20 May 1959, E. A. Willa s.n., (WELT SP050477, AK 249215); Herekopare Island, 4 January 2010, P. B. Heenan s.n, (CHR 609808-609810); Mutton Bird (Titi) Islands, Big Moggy Islands, December 2002, B. D. Rance s.n., (AK 293254). Cultivated (New Zealand): Lincoln, ex Herekopare Island, 2 Feb 1980, H. D. Wilson 798-314, (CHR 368843); Lincoln, ex Long Beach, Landcare Research experimental nursery, 10 July 2008, P. B. Heenan s.n., (CHR 609803).

Distribution

( Fig. 44 ). Endemic. New Zealand. South and Stewart Island/Rakiura. Known from Otago and islands off the coast of Stewart Island/Rakiura Lepidium juvencum is currently known from just three locations: Long Beach and Green Island (Otago Peninsula) and Herekopare Island (east of Stewart Island/Rakiura). However, it is also probably present on some of the south-western Titi Island (south-west of Stewart Island/Rakiura) (B.D. Rance pers. comm.) and it is still likely to occur elsewhere, especially on rat free islands in the vicinity of Stewart Island, as is evidenced by specimens previously col lected from Womans (CHR 261892) and Solander (CHR 253066) islands in the 1960s and 1970s.

Recognition.

Lepidium juvencum is distinguished by open, sprawling, straggling growth habit, and the stems are often trailing on the ground ( Figs 46 , 47 ). The leaves are elliptic, elliptic-oblanceolate, obovate to elliptic-obovate, and have attenuate bases; the marginal teeth are usually small and are mostly confined to the distal third of the leaf ( Fig. 48 ). The silicles are most like Lepidium oleraceum but differ by possessing a rounded, slightly notched apex ( Fig. 49 ).

Ecology.

Lepidium juvencum grows in open and often disturbed sites on sandy soil. At Long Beach it grows on stabilised sand at the base of a cliff immediately behind the beach, and at Herekopere Island it occurred on a steep coastal bank comprising sandy loam. On Kaimohu Island, in the south-western Titi group, what is probably Lepidium juvencum has been recorded growing with Lepidium limenophylax on the margins of coastal scrub. Lepidium juvencum has also been established and is self-seeding at the Yellow-eyed Penguin Trust revegetation project at Tavora Reserve (near Palmerston, North Otago). Here it grows among Euphorbia glauca G.Forst. and Ficinia spiralis (A.Rich.) Muasya et de Lange on sand dunes at the back of the beach.

Conservation Status.

Lepidium juvencum is presently known from three wild localities, and, while the number of plants at these localities is not known with certainty, it is estimated that there are <100 in total. It is also acknowledged that Lepidium juvencum is likely to be more widespread, especially in the vicinity of Stewart Island/Rakiura, and further field surveys are required. Recruitment is likely to be sporadic, and the small and sparse populations are especially vulnerable to stochastic events, such as storm surges, that could erode its habitat. Based on our current knowledge of this species and using the New Zealand Threat Classification System ( Townsend et al. 2008), Lepidium juvencum qualifies as 'Threatened/Nationally Critical’ (either criterion A(1) or A(3) of Townsend et al. (2008) applies). We recommend appending the qualifiers, ‘CD’ (Conservation Dependent - because the species has been deliberately established at Tavora Reserve, where it is actively managed), ‘DP’ (Data Poor - to reflect uncertainty over its distribution), and ‘RR’ (Range Restricted - because it is naturally confined to a geographically small part of the New Zealand Botanical Region).

Figures

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

Figure 45. Holotype of Lepidium juvencum Heenan et de Lange.

Figure 46. Young plant of Lepidium juvencum growing with Poa astonii near shearwater burrows.

Figure 47. Flowering stem of Lepidium juvencum showing multiple inflorescences and trailing growth habit. Scale bar = 20 mm.

Figure 48. (From left to right) basal-, mid- and upper-stem leaves of Lepidium juvencum. Scale bar = 20 mm.

Figure 49. (A) Mature silicle of Lepidium juvencum; (B) close up of silicle apex showing slight notch. AK 297694. Scale bars = 1 mm.