Lepidium oblitum, 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 : 59-67

Lepidium oblitum sp. nov.

A L. panniformo habitu effuso, foliis saepe nitentibus sparse leviter dentatis ab apicibus surculorum confertis et a serie rDNA ETS differt. A. L. oleraceo habitu effuso aestati-virenti, siliculis valde incisuris et a serie rDNA ETS differt.

Holotype.

Chatham Islands ( Fig. 57 ): Chatham Is., Mangere Island, Mangere Island Nature Reserve, South of Hut Landing, 14 February 2006, P.J. de Lange CH876 & P.B. Heenan, AK 300342! Isotypes: CHR 552303A-C!

Etymology.

The epithet " oblitum " from the Latin meaning "forgotten, disregarded or neglected" refers to the circumstances in which this species was first discovered. At an early stage of this revision Lepidium oblitum had been included within the range of Lepidium panniforme , with some plants treated as possible hybrids between Lepidium panniforme and Lepidium oleraceum . It was only following critical analysis of plants grown in New Zealand from samples collected from Mangere Island that the distinctive nature of this species was realized using DNA and morphological data.

Description

( Figs 58 -62 ). Tap-rooted, strongly pungent, sprawling, laxly though much-branched, leafy perennial shrub, forming patches up to 1.0 × 0.9 m. Tap-root up to 700 mm long, ± napiform, branched 1-2 or more times. Rootstock 6-14 mm diam., woody, exposed portion ± smooth, often covered in dried leaf remnants and withered branch stubs. Plants usually dying down to rootstock and/or previous seasons stem nodes, towards end of growing season. Stems mostly seasonal, a few ± persistent (i.e. lasting 2 or more years), arising from rootstock base and basal portion of main central stem, widely and unevenly spaced or closely packed, woody, lax and sprawling, sometimes arching and subascendent, weakly angled to ± terete, glabrous; mature stems 2.1-4.6 mm diam., 0.3-0.8 m long; green to yellow-green, brittle, bases bearing numerous leaf abscission scars, otherwise devoid of leaves for at least the first ⅔ with the final ⅓ distinctly leafy and often much branched when vegetative, with the leaves tending to fall at flowering and fruiting; upper stems similar, though distinctly leafy and pliant. Leaves coriaceous, fleshy, green to dark green, often glossy. Rosette leaves 5-14(-20), mostly present in autumn - early spring usually not persisting (very rarely so) at fruiting; petioles distinct, up to 40 × 2 mm, flat or slightly concave in cross-section, succulent; lamina oblanceolate, cuneiform, obovate-oblong to spathulate up to 60 × 22 mm, margins finely to deeply incised in upper ¼ -⅓, teeth in 3-6(-8) pairs running to praemorse apex, basal few teeth pair usually asymmetric, base narrowly attenuate. Middle stem leaves mostly persisting at fruiting; petiole up to 32 mm long, mostly flat in cross-section, sometimes slightly concave, usually winged; lamina narrowly oblanceolate, oblanceolate, spathulate, oblong, obdeltoid, 15.0-32.0(-56.2) × 12-16.8(-18.6) mm; margins finely to deeply incised in distal ¼ -⅓, teeth in 3-6(-8) pairs running to the usually praemorse apex, basal few teeth pairs usually asymmetric, lamina base narrowly attenuate, extending as a wing (0.8-1.2 mm wide) usually to petiole base. Upper stem leaves petiolate, petiole 12 mm long, flat or slightly concave, usually broadly winged; lamina narrowly oblanceolate, narrowly lanceolate, narrowly spathulate, to linear-cuneiform, 10.2-20.0(-29.0) × 2.4-3.5(-4.8) mm; margins entire or deeply dentate, if dentate then usually asymmetrically tridentate (rarely with 1-4 teeth), lamina base narrowly attenuate, extending as a wing (0.3-1.7 mm wide) almost to petiole base. Racemes (30-)50(-76) mm long, usually congested, elongating up to 100 mm at fruiting, terminal and axillary; rachis and pedicels glabrous (pedicels very rarely bearing a few minute, caducous, glandular hairs near base); pedicels, erecto- patent to patent, 0.4-0.8(-1.0) mm long, elongating to 0.8-1.2(-2.0) mm long at fruiting. Flower buds dark green to green, apex glabrous. Flowers sweetly fragrant, 1.6-1.8(-2.0) mm diam. Sepals 4, saccate, pale to dark green with a broad white, ± undulose margin, pale to dark green with a broad white, ± undulose margin, deeply concave, adaxially weakly keeled or not; lateral sepals 0.9 × 0.6 mm, broadly ovate to oblong, ± overlapping at base, apex rounded to obtuse, adaxial surface glabrous (sometimes diffusely papillate), abaxial surface usually glabrous, sometimes hairy near base, hairs patent, weakly flexuous, 0.1-0.3 mm long, eglandular, shedding at anthesis; median sepals 1.0 × 0.9 mm, broadly ovate to oblong, apex rounded to obtuse, adaxial surface glabrous, abaxial surface glabrous. Petals overtopping sepals, white, 0.9-1.15(-1.3) × 0.5-0.6(-0.8) mm, patent, clawed; limb broadly obovate, apex weakly retuse. Stamens 2-4, equal. Anthers c. 0.10 mm long. Pollen bright yellow. Nectaries 2, subulate, 0.3-0.42 mm long. Silicles cartilaginous when fresh, coriaceous when dry, orbicular, orbicular-ovate to ± rhomboid, (2.8-)3.0(-3.3) × (2.4-)2.6(-3.0), margin winged, notably more so toward apex, apex notched, base obtuse, valves green maturing yellow-green, glabrous, dried surface ± coarsely reticulate; style 0.1-0.2(-0.3) mm long, free from the narrow wing, usually exceeding the notch; stigma 0.18-0.22 mm diam, capitate. Seeds 2, ovoid to ellipsoid, orange-brown to dark red-brown, not winged, 1.8-1.9 × 0.9-0.93 mm. FL Nov-Mar. FR Jan-Jun.

Representative Specimens.

Chatham Islands: Rabbit Island, 14 February 2006, P.J. de Lange CH878 & P.B. Heenan, (AK 300344). Mangere Island, Mangere Island Nature Reserve, Above Hut, 14 February 2006, P.J. de Lange CH874 & P.B. Heenan, (AK 300340; CHR 552373); Mangere Island, Mangere Island Nature Reserve, 'Top Plateau’, 22 February 2011, B. Gibb s.n., (AK 331585).

Distribution

( Fig. 63 ). Endemic. New Zealand, Chatham Is., Mangere and Rabbit Islands.

Recognition.

Lepidium oblitum is recognised by its sprawling growth habit ( Fig. 58 ); by the branches often widely spaced, trailing and mostly devoid of foliage except for the ends which are typically densely terminated by foliage ( Fig. 57 ); and by the prominently notched silicles ( Fig. 62 ). Of those species with which it grows ( Lepidium oligodontum , Lepidium oleraceum , Lepidium panniforme and Lepidium rekohuense ), it can be easily distinguished from Lepidium oleraceum by its sprawling growth habit, flowers with 2-4 stamens, and distinctly notched silicles ( Figs 58 , 61 , 62 ).

From Lepidium oligodontum , Lepidium oblitum is easily distinguished by it’s more upright, though somewhat, untidy, sprawling growth habit ( Fig. 58 ), and longer lived, persistently leafy branches. The foliage of Lepidium oblitum ( Figs 59 , 60 ) has leaf margins that are consistently toothed (never sparingly-toothed or entire), while the flower ing racemes are distinctly longer ((30-)50(-76) mm cf. (5.0)-9.7(-28.9) mm in Lepidium oligodontum )) and on fruiting they may elongate up to 100 m (rather than 60 mm). In Lepidium oblitum the flowers have 2-4 rather than 2-4-6 stamens ( Fig. 61B, 61C ), while the silicles are never fleshy or turgid, rather they are distinctly cartilaginous and prominently (rather than weakly) notched ( Fig. 62 ). Lepidium oblitum also has consistently shorter styles ((0.1-0.2(-0.3) mm long) than Lepidium oligodontum ((0.2-0.8(1.2) mm long)).

Lepidium oblitum and Lepidium panniforme grow together on Mangere Island ( Fig. 63 ). As they have similar silicles and flowers with 2-4 stamens but very different foliage, Lepidium oblitum was initially thought to be hybrid between Lepidium panniforme and Lepidium oleraceum . At that time it was not realised how widespread Lepidium oblitum is, nor that it comprised stable, true-breeding populations (G. Houliston unpubl. data). It was only following DNA-based investigations undertaken for this paper that the putative hybrid status was rejected and its status as a species recognised. Nevertheless, Lepidium oblitum is still closely allied to Lepidium panniforme , and both also share a relationship to the extinct Lepidium obtusatum , a relationship evident by all three species sharing prominently notched silicles. Lepidium oblitum has widely spreading, lax (rather than erect to suberect), sprawling stems and rosette leaves that distinguish it from Lepidium panniforme ( Figs 82 , 83 ). The leaves of Lepidium oblitum are shallowly toothed but they are never as deeply serrated or lacerate as those of Lepidium panniforme ( Figs 81 , 83 , 84 ). DNA data suggests that gene flow between Lepidium oblitum and Lepidium panniforme has occurred at some sites on Mangere Island (G. Houliston unpubl. data).

Lepidium oblitum also grows with Lepidium rekohuense on Rabbit Island. From that species it is easily separated by its smaller growth habit; by the glabrous rather than sparsely papillate-hairy upper branch stems, and glabrous rather than finely hairy inflorescences (the pedicels of Lepidium oblitum may, very rarely, bear a few caducous glandular hairs). Fur thermore, the flowers of Lepidium oblitum have 2-4 rather than 2 stamens, while the silicles of Lepidium rekohuense are also mostly orbicular (rarely obovate) and slightly larger (up to 4.1 × 4.0 mm cf. 3.3 × 3.0 mm).

Ecology.

Lepidium oblitum is one of three Lepidium species recorded from Mangere and Rabbit islands. On these islands, it is frequently found growing in association with petrel burrows, and on exposed, often wind eroded cliff faces, associated soil blowouts and ephemeral drainages and seepages. On Mangere Island, it is perhaps most common among the boulders and rocks forming the northern summit of the Top Plateau. In these habitats, Lepidium oblitum commonly grows with Asplenium obtusatum , Festuca coxii (Petrie) Hack., Disphyma papillatum Chinnock, Puccinellia chathamica (Cheeseman) Allan et Jansen and Senecio radiolatus F.Muell. subsp. radiolatus. On Mangere Island, it is also associated with Aciphylla dieffenbachii (F.Muell.) Kirk, Hebe chathamica (Buchanan) Cockayne et Allan, Hebe dieffenbachii (Benth.) Cockayne et Allan (and hybrids between these two Hebe ), Myosotidium hortensium (Decne.) Baill., and, on occasion, Lepidium oleraceum and Lepidium panniforme . On Rabbit Island it is associated with Atriplex australasica Moq., Critesion murinum (L.) Á.Löve subsp. murinum, Malva arborea L., Lepidium oligodontum and Lepidium rekohuense .

Conservation Status.

Lepidium oblitum is so far known only from the Chatham Islands group where it has been collected from Mangere and Rabbit Islands ( Fig. 63 ). On Mangere Island (a Nature Reserve, with strict permit controlled access) it is known from several populations, the largest of which occurs along the northern western cliff faces of 'Top Plateau’. That population may number in the tens of plants; the only other ones known occur in steep runnels draining the western cliffs south of the main Landing area. When visited by PdL and PBH in 2006, there were fewer than 10 adults in total. Subsequent visits to Mangere Island by Department of Conservation rangers suggest that there has been little change in the population sizes on that island. However, hard data is unavailable and so it would inappropriate to infer from these observations that Lepidium oblitum populations on Mangere Island are stable. On nearby privately owned Rabbit Island, two plants of Lepidium oblitum were seen in 2006 and the island has not been visited by Department of Conservation staff since.

Therefore, based on available information Lepidium oblitum is known from two sites, totalling 4 populations, which collectively are unlikely to exceed 100 mature individuals. Further, the total area of occupancy is considerably less than 1 ha. On the basis of that data, using Townsend et al. (2008), Lepidium oblitum qualifies as " Nationally Critical" (using either criterion A(1) or A(3)) because there are fewer than 250 mature individuals known and the total area of occupancy is ≤ 1 ha. We favour criterion A(3) because a precise survey of the numbers of plants of Lepidium oblitum has yet to be carried out, and available data (beyond that obtained by PdL and PBH) is unreliable because of understandable past confusion with Lepidium oleraceum s.s. and Lepidium panniforme .

This conservation assessment should also be qualified ‘CD’ (Conservation Dependent) because Mangere Island is subject to ecological restoration, and ongoing surveillance to ensure it remains predator-free. Should rodents establish on the island, they will affect that island’s Lepidium species, both directly through browse and indirectly through predation of the sea birds that maintain this species habitat. Other necessary qualifiers include ‘DP’ (Data Poor) because of the lack of precise information on population size and trend data, ‘IE’ (Island Endemic), and ‘RR’ (Range Restricted) because of its precise habitat requirements and geographically narrow-range.

Figures

Figure 57. Holotype of Lepidium oblitum Houliston, Heenan et de Lange.

Figure 58. Wild plant of Lepidium oblitum showing growth habit of plant associated with Myosotidium hortensium, Disphyma papillatum and Festuca coxii in petrel colony on Mangere Island (image: G. A. S. Taylor).

Figure 59. (From left to right) rosette and basal- to mid-stem leaves of Lepidium oblitum. (AK 300342). Scale bar = 20 mm.

Figure 60. Cultivated plant of Lepidium oblitum showing rosette leaves.

Figure 61. A Upper stem leaves and inflorescence of Lepidium oblitum B flowers showing arrangement of sepals, petals, androecia and gynoecia C close-up of flower.

Figure 62. Mature silicle of the holotype of Lepidium oblitum (AK 300342). Scale bar = 1 mm.

Figure 63. Distribution of Lepidium oblitum, Lepidium oligodontum, Lepidium panniforme and Lepidium rekohuense.

Figure 81. Holotype of Lepidium panniforme de Lange et Heenan.

Figure 82. Wild plant of Lepidium panniforme on Mangere Island showing growth habit (image: B. Gibb).

Figure 83. Vegetative stems and inflorescences of Lepidium panniforme.

Figure 84. (From left to right) basal- and mid-stem leaves of Lepidium panniforme. Scale bar = 20 mm.