Lepidium panniforme, 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 : 92-97

Lepidium panniforme sp. nov.

A L. oleraceo habitu renascenti, habenti periodo distincto rosulato, foliis valde dentatis vel laceratis, siliculis late orbiculatis vel orbiculato-rhomboideis minute alatis ed emarginatis et serie DNA differt. A L. oligodonto et L. rekohuensi habitu suberecto vel erecto fruiticoso, foliis semper dentatis vel laceratis, floribus (2-)4-staminatis et serie DNA differt.

Holotype.

Chatham Islands ( Fig. 81 ): Mangere Island, Mangere Island Nature Reserve, Mangere Island, 23 November 2000, M. Thorsen, AK 255607! Isotype: CHR!, K!

Etymology.

The name " panniforme " from the Latin meaning "like a shredded rag" (N. G. Walsh pers. comm.) refers to the ragged appearance of the deeply lacerate, tattered basal and lower stem leaves characteristic of this species.

Description

( Figs 82 -85 ). Tap-rooted, pungent-smelling, summer-green, perennial herbarising from stock rootstock 7.3-8(-10) mm diam. Growth habit, erect to suberect, loose to densely branched plants up to 1 m across. Stems ± persistent, sometimes dying down to rootstock over winter or in times of adversity; upright to spreading, bases often very stout, ± spherical, somewhat woody when mature 10-15 × 10-12 mm, comprised of numerous old leaf and stem bases, sometimes producing roots, new seasons grow erect to suberect, glabrous, sometimes with very sparse, appressed, caducous, silky 0.5-1 mm long, hairs near stem apices; at fruiting stems often devoid of foliage for 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, 20-35(-40) × 2-9 mm. Lamina oblanceolate, lanceolate, narrowly lanceolate (rarely spathulate), 50-100 × 10-30 mm; either deeply toothed and/or lacerate or with distal ⅔ to ⅓ deeply toothed and/or deeply lacerate, teeth in 10-18(-20) pairs, blunt to sharp, running to and including apex and usually extending beyond leaf outline, base cuneate to narrowly cuneate. Middle stems leaves usually with indistinct petioles, these 10-30 mm long; lamina narrowly linear-lanceolate to linear, often recurved to falcate from or near ½ to ⅓ of leaf length, 50-80(-120) × 3-6 mm; margins deeply lacerate and/or toothed, teeth usually prominent, often confined to the upper ⅔, in 12-18(-30) pairs, these running to and including the apex; 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, usually toothed and/or lacerate, patent or recurved and/or falcate for upper ½ of leaf length, 30-50(-100) × 2.0-3.0(-30) mm. Racemes (5-)10-15 mm long, terminal and axillary; rachis glabrous; pedicels glabrous, erecto-patent, 2-5(-8) mm long at fruiting. Flowers c.0.4-0.8(-1.0) mm diam. Sepals glabrous or finely pubescent, or with both states within the one flower, green, broadly ovate to oval, c.0.6-1.0 × 0.6-1.2 mm, with pale-green to white thickened margin, apex broadly obtuse. Petals white, 1.5-2.0 × 0.3-0.8(-1) mm, erecto-patent to somewhat spreading, clawed; limb narrowly obovate, apex obtuse, occasionally emarginated. Stamens (2-)4, equal. Nectaries 2, subulate, 0.35 mm long. Silicles cartilaginous when fresh, coriaceous when dry, orbicular, orbicular-rhomboid (2.5-)3.0-3.5 × (1.5-)1.8-2.5(-3.3), slightly winged in upper ⅓, apex minutely notched, based obtuse to ± cordate, valves glabrous, dried surface often distinctly reticulate; style 0.1-0.2(-0.3) mm long, free from the narrow wing, exceeding the shallow notch; stigma 0.2-0.3 mm diam., capitate. 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.

Chatham Islands: Mangere Island, Mangere Island Nature Reserve, August 2005, D. Prendeville s.n., (AK 293305); Mangere Island, Mangere Island Nature Reserve, February 2006, B. Gibb s.n., (AK 295945); Mangere Island, Mangere Island Nature Reserve, 14February 2006, P. J. de Lange CH877 & P. B. Heenan, (AK 300343); Mangere Island, Mangere Island Nature Reserve, 14 Feb 2006, P. J. de Lange CH874 & P. B. Heenan,(AK 300340); Mangere Island, Mangere Island Nature Reserve, 14 Feb 2006, P. J. de Lange CH875 & P. B. Heenan, (AK 300341). Rekohu Petre Bay, Waitangi Village, near Council Buildings, (Naturalised) 19 September 2007, P. J. de Lange CH976 & P. B. Heenan, (AK 300992). Cultivated (New Zealand): Auckland, Manurewa, ex Mangere Island, Auckland Botanic Gardens, July 2002, P. J. de Lange 5513, (AK 258042); Lincoln, ex Mangere Island, Landcare Research experimental nursery, 10 July 2008, P. B. Heenan s.n., (CHR 609807); Lin coln, ex Mangere Island, Landcare Research experimental nursery, 25 January 2010, P. B. Heenan s.n., (CHR 609812).

Distribution

( Fig. 63 ). Endemic. New Zealand, Chatham Islands, where it is only known from Mangere and Little Mangere Island. In 2007, Lepidium panniforme was collected once growing in the loose gravel of a car park near the Chatham Island Council Buildings, Waitangi, Rekohu. Those plants had probably established from seed that was accidentally discarded there by PdL and PBH while pressing freshly gathered fruiting specimens in 2006.

Recognition.

Lepidium panniforme has an erect, suberect, or spreading growth habit ( Figs 82 , 83 ), which immediately separates it from the decumbent Lepidium oligodontum , and Lepidium rekohuense . It is further separated from these taxa by the long persistent, much larger, usually deeply toothed or lacerate and often rather tattered basal and lower stem leaves ( Figs 81 -84 ), and from Lepidium oligodontum and Lepidium rekohuense by the flowers which consistently have (2-)4 stamens. In growth habit, the species is most similar to Lepidium oblitum and Lepidium oleraceum ,species with which it grows on Mangere Island. The key distinctions between Lepidium oblitum and Lepidium panniforme are described under Lepidium oblitum , however; in brief, the deeply toothed and/or lacerate leaves of Lepidium panniforme serve to readily distinguish it from Lepidium oblitum . From Lepidium oleraceum it is also easily separated, especially when fruiting when the notched rather than acute silicle apex can be seen, but also when vegetative, as the leaves of Lepidium panniforme are diagnostically deeply toothed and/or lacerate. This is a condition seen otherwise only in the Bounty Islands endemic Lepidium seditiosum which differs by having hairy inflorescences ( Fig. 96 ) and distinct rDNA ETS sequence. Lepidium panniforme shares the same rDNA ETS sequence as the morphologically different Lepidium obtusatum . From that species it is recognised by its upright shrub-habit, deeply lobed to lacerate leaves and much smaller, minutely notched silicles.

Ecology.

On the highly modified landscape that is Mangere Island, Lepidium panniforme is known only from a very few sites where it grows in coastal herbfield along cliff tops, in rough pasture, shrubland, regenerating forest and sites kept artificially open, such as track sides. Because Mangere Island is being actively restored to coastal forest, few of these habitats are natural, and as such it is difficult to determine what the real habitat preferences of Lepidium panniforme are. However, in less modified parts of the island, plants are mainly confined to the steeper, often heavily seabird burrowed slopes and cliff margins. Here, plants mostly grow amongst coxella ( Aciphylla dieffenbachii ), Hebe chathamica , Chatham Island forget-me-not ( Myosotidium hortensium ), Chatham Island sow thistle ( Embergeria grandifolia (Kirk) Boulos) and, in places, Lepidium oblitum . Little is known about the habitat preferences of Lepidium panniforme on Little Mangere Island. The only records of its presence there are a series of photographs taken by the late D.V. Merton in February 2006 which show it present on the forest floor within canopy gaps in the summit forest. One assumes that, as with nearby Mangere Island, it also grows on cliff faces, rock ledges are within other suitably open sites within the coastal shrubland and herbfield of that precipitous island.

Conservation Status.

It is notable that while Lepidium oligodontum and Lepidium rekohuense are present in the earliest Lepidium collections made by Travers, Cockayne and Martin from the Chatham Islands, Lepidium panniforme is absent. The first records of it are those gatherings and photographs taken by staff of the former Wildlife Service from Mangere and Little Mangere Island during the 1960s and 1970s. Based on these obser vations, Lepidium panniforme is naturally confined to Mangere and Little Mangere Island. On Mangere Island it is known with certainty only from the vicinity of the hut and along the track from there across to the isthmus. In 2006, c.60 individuals were seen in these areas.

Subsequent field work by Department of Conservation staff on Mangere Island indicates that Lepidium panniforme is a very uncommon species, which is potentially further threatened by the re-vegetation of that island. This is in part a natural process, though it is one which has been augmented by deliberate plantings as part of that island’s long term restoration management as a wildlife refuge for threatened endemic fauna (D. Houston pers. comm.). Nevertheless replanting within the Lepidium panniforme siteshas been carefully managed to date, and the species remains locally abundant along the disturbed and open track margins from the hut to the isthmus. However, with such a small population Lepidium panniforme remains vulnerable to any change in management, and, over time as the surrounding shrubland matures to forest, some decline through natural succession is to be expected. Therefore, this remarkable species will need to be closely monitored to ensure that it is not lost from the island. There is also a need to survey for the species on the almost inaccessible, closely adjacent Little Mangere Island, as the species is still known from there only from those few images taken by the late D.V. Merton.

Therefore, with <250 mature plants known, and a total area of occupancy of <1 ha, using the New Zealand Threat Classification System (see Townsend et al. 2008), Lepidium panniforme is rated as 'Threatened/Nationally Critical’. In this case criterion A(1) or A(3) equally apply. To that listing we recommend appending the qualifiers, ‘CD’ (Conservation Dependent - as the species is being actively managed), ‘DP’ (Data Poor - because accurate information about its status on Little Mangere Island is still needed), ‘IE’ (Island Endemic), ‘OL’ - because the species occurs on two closely associated islands such that it is at risk of elimination through catastrophe), and “RR” (Range Restricted - because of the narrow geographic range this plant occupies in relation to the rest of the New Zealand Botanical Region).

Figures

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.

Figure 85. Mature silicle of Lepidium panniforme from holotype (AK 255607). Scale bar = 1 mm.

Figure 96. Close up of inflorescence of holotype of Lepidium seditiosum (OTA 59718) showing hairy rachises and pedicels, and immature silicles. Scale bar = 1 mm.