Lepidium seditiosum, 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 : 104-107

Lepidium seditiosum sp. nov.

A L. oleraceo rachidibus inflorescentiae et pedicellis hirsutus et a serie rDNA ETS differt. A L. panniformo floribus 4-staminatis praeterea differt.

Holotype.

Bounty Islands ( Fig. 93 ): Bounty Islands, Funnel Island, n.d.J. Amey s.n, OTA 59718!

Notes:

Lepidium seditiosum is known only from the holotype collection, which was collected sometime in 2004 ( Amey et al. 2007).

Etymology.

The epithet ' seditiosum ' derived from the Latin ' seditio ' (meaning: dissension, insurrection, mutiny, rebellion), alludes to the mutiny of the majority of Lieutenant William Bligh’s crew on the 28 April 1789. In 1788, some months before the rebellion, Bligh had discovered and named the Bounty Islands taking the name from his ill-fated ship The Bounty.

Description

( Figs 94 -96 ). Erect, perennial herb. Stems sparse, erect; mature stems long, 4.14-4.41 mm diam. stout, woody, rigid, ± square, prominently angled, bases much covered in leaf abscission scars, middle and upper portion leafy. Leaves fleshy, dark green, stem leaves evidently withering with age; petiole distinct, 14-22.0 × 1.9-2.6 mm, decurrent, prominently channelled, broadly winged, with a broadly sheathing base; lamina variable 32.4-45.4 × 21.2-26.4 mm decreasing in size toward inflorescences, broadly elliptic, elliptic to oblanceolate; apex praemorse or tridentate; margin coarsely and ± regularly dentate to deeply incised; teeth protruding beyond leaf outline; in 8-12 uneven pairs, up to 5.3 mm deep, increasing in size toward apex; base broadly attenuate tapering, extending into a broad petiole wing. Inflorescences immature but evidently racemose, rachis 1.3-1.5 mm diam., terminal and lateral, leaf-opposed, densely and mostly circumferentially covered in 0.4-0.6 mm long, white, clavate hairs; pedicels 1.6-2.2 mm long at flowering, erecto-patent, densely and mostly circumferentially covered in 0.4-0.6 mm long, white, clavate hairs. Flowers 2.3-2.6 mm diam. Sepals 4, saccate, dark green usually with a narrow white, ± undulose margin; lateral sepals broad, 0.8-1.2 mm diam., obovate to broadly obovate, ± overlapping at base, apex rounded to obtuse, abaxial surface densely hairy, hairs 0.1-0.4 mm long, eglandular or glandular, mostly clavate, some setose, median sepals 0.8-1.0 mm diam., broadly obovate, dark green, usually with a narrow white, ± undulose margin, apex rounded to obtuse, abaxial surface densely hairy, hairs 0.1-0.4 mm long, eglandular or glandular, mostly clavate, some setose. Petals white, 1.3-2.0 × 1.0-2.3 mm, mostly recurved over stigma some spreading, claw 0.4-0.9 mm long; limb obovate, obovate-spathulate rarely orbicular, apex obtuse or slightly emarginate, margins smooth. Stamens 4, filaments 1.2-1.8 mm long, white; anthers 0.3-0.4 mm long, yellow. Ovary 1.1-1.8 × 0.6-1.3 mm, broadly ovate to elliptic, dark green, apex round or weakly notched; style 0.11-0.4 mm long, cylindrical below, broadly spreading at apex; stigma 0.2-0.4 mm diam. Nectaries 4, 0.2-0.3 × 0.1-0.15 mm, narrow-oblong, pale translucent green. Mature silicles not seen. FL Nov. FR unknown.

Distribution

( Fig. 76 ). Endemic. Bounty Islands (Funnel Island, Molly Cap).

Recognition.

Amey et al. (2007) initially reported the presence of Lepidium oleraceum s.l. from the remote Bounty Islands. In that paper they noted that unpublished rDNA ETS data from their gathering placed the Bounty Islands plant within a southern Lepidium oleraceum clade of samples collected from Banks Peninsula south to Stewart Island rather than plants from the nearby Antipodes Islands. On the basis of that information they suggested that the Bounty Islands plant was a recent arrival, probably coming from the Otago coastline of the southern South Island. Subsequently, the rDNA ETS phylogeny presented here confirms that Lepidium seditiosum is related to the South Island species Lepidium aegrum , Lepidium crassum , and Lepidium juvencum ( Fig. 2 ). However none of these species are morphologically similar to Lepidium seditiosum . Morphologically, the most similar species is the Chatham Islands endemic Lepidium panniforme , which also has deeply toothed (though also lacerate leaves) but whose stems and inflorescence rachis are glabrous (only very rarely furnished with sparse silky hairs), and whose rDNA ETS sequence places it as sister to Lepidium obtusatum . The Bounty Islands plant differs from Lepidium panniforme (and indeed all other members of the Lepidium oleraceum complex) by its distinctly clavate-hairy upper stems and inflorescence rachises.

While our material is inadequate to furnish a full species description, the absence of mature silicles and basal leaves should not preclude formal taxonomic recognition. The Bounty Islands are perhaps the most remote outlier of the New Zealand Archipelago, and are very rarely visited ( Amey et al. 2007), so the alternative, of waiting for better fruiting material before describing what in our view is clearly a new species is, unacceptable. In the authors’ opinion, there is sufficient data available to justify this plant’s taxonomic recognition at species rank.

Ecology.

Prior to the remarkable discovery of Lepidium on the Bounty Islands group, these islands had always been considered devoid of any form of terrestrial vegetation beyond a few lichens and algae ( Amey et al. 2007). None of the 15 islands, islets and rock stacks comprising the group reach any higher than 88 m a.s.l., and virtually all available dry land is occupied by some of the densest concentrations of nesting seabirds seen anywhere in the world ( Amey et al. 2007). Amey et al. (2007) recorded Lepidium seditiosum (as Lepidium oleraceum s.l.) as growing within rock crevices near the summits of one island (Funnel Island) and an inaccessible (by boat) rock stack (Molly Cap) within the Bounty Islands group. At the time of their discovery, on Funnel Island plants grew on the margins of a colony of nesting seabirds, in a site inaccessible to albatross and penguins but used by Fulmar prions (Pachyptila crassirostris) and possibly Cape pigeons (Daption capense). They noted that where the plants grew, a 'rich friable soil’ had accumulated, and that the crevice walls provided some shelter from the most extreme winds. Because of the inaccessible nature of Molly Cap, no further observations on the plant they had seen from their boat could be made.

Conservation Status.

Amey et al. (2007), during a November 2004 visit to the Bounty Islands group, recorded 'at least 13' plants at two sites (Funnel Island (12 plants) and Molly Cap (1 plant). On this basis, Lepidium seditiosum qualifies as 'Threatened / Nationally Critical’ (either criterion A(1) or A(3) of Townsend et al. (2008)) as there are fewer than 250 mature plants known and the total area of occupancy is <1 ha. To this assessment we add the qualifiers ‘CD’ (Conservation Dependent - as the Bounty Islands are a Nature Reserve and World Heritage Site with strict controls in place to regulate landings, and prevent the spread of diseases, weeds and foreign predators), ‘DP’ (Data Poor - because accurate data on the total number of individuals and trend data is not available), ‘IE” (Island Endemic), and ‘OL’ (One Location - because, following the definition in Townsend et al. (2008), the species is confined to the Bounty Islands group, where it grows on an island and rock stack in close proximity, and so the chances of losing the species to a single event are greater than for a species found in one island group on several widely separated islands).

Figures

Figure 2. Maximum likelihood phylogeny of ETS 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. The main clade branches have been truncated to accommodate the tree within the journal format. AUS = Australia, NZ = New Zealand.

Figure 76. Distribution of Lepidium oleraceum and Lepidium seditiosum.

Figure 93. Holotype of Lepidium seditiosum de Lange, Heenan et J. Rolfe.

Figure 94. Lepidium seditiosum growing in granite crevice on summit of Tunnel Island, Bounty Islands (image: J. Amey).

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.