Lepidium obtusatum Kirk, Trans. et Proc. New Zealand Inst. 24, 423, (1892)

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 : 67-71

Lepidium obtusatum Kirk, Trans. et Proc. New Zealand Inst. 24, 423, (1892)

Holotype.

New Zealand ( Fig. 64 ): Port Nicholson, n.d., Miss Kirk, WELT SP030109!

Notes:

Kirk’s protologue for Lepidium obtusatum states "Hab. North Island: Maritime rocks at the entrance to Port Nicholson, Miss Kirk" ( Kirk 1892). Only one herbarium sheet annotated ' Lepidium obtusatum n.s., Port Nicholson, Miss Kirk ' and so matching the protologue as to name, collector (Miss [Lily] Kirk), type locality, and labelled in the naming authors hand could be located in the WELT (the main herbarium where Kirk material has come to be lodged) so this sheet is regarded here as the holotype.

Etymology.

Although the exact meaning of the species " obtusatum " was not given by Kirk (1891) it seems that he took the name from the shape of the hypogynous glands (i.e. the nectaries) which he specifically noted ( Kirk 1899) are "very short and obtuse".

Description

( Figs 65 -68 ): Glabrous, prostrate, much-branched, succulent, rhizomatous, perennial herb, forming patches up to c. 1 m diam. Stems 200-300 × 3-6 mm, prostrate, succulent, flexuous, widely spreading, leafy along stems. Leaves glabrous, thick, succulent and very coriaceous, dark glossy green, variable in size and shape. Rosette leaves 50-80 × 15-20 mm, elliptic to elliptic ovate, oblong, oblong-spathulate; apex, obtuse or rounded, crenate-serrate with 3-4 blunt teeth; margin crenate, crenate-serrate, sometimes weakly bidentate, rarely entire, with 0-24 pairs of teeth; teeth up to 1.8 mm deep, mostly regular size, not protruding beyond leaf outline; base narrowly attenuate to cuneate, ± decurrent, petiole distinct, 32-40 × 1.6-2.9 mm, slightly winged, or not, channelled. Cauline leaves similar to rosette leaves but smaller (up to 42.3 × 13.3 mm), persistent; petioles distinct, and more consistently and conspicuously winged. Upper stem leaves much reduced; lamina 8.8-16.8 × 5.4-8.8 mm, broadly oblanceolate, spathulate, obdeltoid to suborbicular, apex obtuse, usually with 1 prominent and 2 smaller blunt teeth with rounded to obtuse apices (teeth not protruding beyond leaf outline); margin crenate to dentate or entire, if teeth present these in 2-6 pairs, usu ally blunt ended sometimes subacute, up to 1.2 mm deep, base broadly cuneate to attenuate, petiole distinct, often appearing sessile, usually broadly winged, up to 6 mm long, channelled. Inflorescence terminal and lateral, usually obscured by associated leafy stems, racemose; racemes 9.9-45.6 mm long, rachis 0.6-0.9 mm; pedicels 2.8-3.2 mm long at flowering, erecto-patent, elongating somewhat after anthesis, glabrous. Flowers 4.3-5.0 mm diam. Sepals 4, saccate, overlapping at base, green, apex obtuse, margin white, shape and size dimorphic; lateral sepals 2.2-2.9 × 2.1-3.0 mm, orbicular, mostly glabrous, sometimes sparsely hairy, hairs 0.2-0.4 mm long, caducous; median sepals 1.9-2.9 × 1.5-1.7 mm, elliptic to obovate, abaxial surface glabrescent, sparsely hairy, hairs 0.2-0.4 mm long, caducous. Petals white, 1.3-1.8 × 1.3-1.8 mm, erect, claw minute, 0.2-0.3 mm; limb orbicular, apex obtuse. Stamens 4, ± equal lengths, 1.2-1.8 mm long, base 0.6-1.0 mm wide; anthers 0.6-0.8 mm long, yellow, pollen yellow. Ovary 1.3-1.8 × 1.3-1.7 mm, broadly ovate to suborbicular green, apex distinctly notched; style 0.3-0.5 mm long, cylindrical below, spreading at apex; stigma 0.5-0.6 mm diam. Nectaries 4, green, 0.12-0.14 × c. 0.09 mm, narrow oblong, apex obtuse. Silicles 4.9-6.4 × 4.2-4.9 mm, broadly ovate, oval-rhomboid to obovate, apex prominently notched, valves yellow-green in dried specimens, glabrous, slightly winged; style 0.2 -0.5 mm long, not or only slightly exserted. Seeds 2.0-2.7 × 1.8-2.0 mm, obovate, broadly obovate, brown to orange-brown, not winged. FL Jul-Jan. FR Jul-Jan.

Representative Specimens.

New Zealand: Entrance to Port Nicholson, n.d., T. Kirk s.n., (AK 4476); Entrance to Port Nicholson, between the outer signal station and Worser Bay, 8 March 1892, T. Kirk 363, (WELT SP030102); Port Nicholson, July 1914, B. C. Aston s.n., (AK 4475, WELT SP030108); Seatoun, July 1919, A. Wall s.n., (CHR 329224); Seatoun, 26 November 1920, W. R. B. Oliver s.n., (WELT SP030107); Seatoun, 1931, J. H. MacMahon s.n., (WELT SP081922, WELT SP081925, WELT SP081926); Seatoun, 28 February 1937, W. R. B. Oliver s.n., (WELT SP030105); Seatoun, 3 December 1938, H. H. Allan s.n., (CHR 21596); Wellington Harbour, Point Dorset, 1939, R. K. Ward s.n., (CHR 464546, WAIK 9680); Seatoun, Breaker Bay, near Fort Dorset, 1951, E. Bishop s.n., (AK 250616).

Distribution

( Fig. 44 ). Endemic. New Zealand, North Island, Wellington Harbour, Miramar Peninsula, in a small area of coastline between Worser Bay and Breaker Bay.

Recognition.

Kirk (1899), Allan (1961), Garnock-Jones (1988) and Garnock-Jones and Norton (1995) considered that Lepidium obtusatum was closely related to Lepidium banksii . From that species, Lepidium obtusatum is distinguished by the prostrate, rhizomatous ( Figs 64 , 65 ) growth habit, less deeply serrated (usually crenate to shallowly toothed) rosette and cauline leaves ( Figs 64 , 66 ), much smaller broadly oblanceolate, spathulate, obdeltoid to suborbicular, usually crenate margined upper stem leaves ( Fig. 67 ), glabrous pedicles and emarginate shortly-winged silicles ( Fig. 68 ). In this paper we have split west Auckland plants previously treated as Lepidium obtusatum into a new species, Lepidium amissum ( Figs 16 -20 ). From that species, Lepidium obtusatum differs by its rhizomatous, prostrate growth habit, flexuose stems ( Fig. 64 ), less deeply toothed (usually crenate-margined) rosette and cauline leaves ( Figs 65 , 66 ) which usually wither at flowering and fruiting, broadly oblanceolate, spathulate, obdeltoid to suborbicular, usually crenate margined upper stem leaves ( Fig. 67 ), and inconspicuous inflorescences which are typically obscured by foliage and associated vegetative stems ( Fig. 64 ). However, both species have similar shaped silicles ( Figs 20 , 68 ), though those of Lepidium amissum are slightly smaller and narrower. Lepidium obtusatum and Lepidium panniforme have the same ETS sequence but are very different plants: from Lepidium obtusatum , Lepidium panniforme differs by its non-rhizomatous, upright shrubby growth habit, much larger, deeply lobed to lacerate leaves, and much smaller, unwinged and only slightly notched fruit. Our rDNA ETS data also suggests that Lepidium oblitum is related to Lepidium obtusatum though, again, they are very different plants ( Figs 57 -63 ( Lepidium oblitum ) cf. Figs 64 -68 ( Lepidium obtusatum )). Lepidium oblitum differs from Lepidium obtusatum by its non-rhizomatous growth habit, much larger, prominently toothed (never crenate) leaves and much smaller silicles.

Ecology.

Very little is known about the habitat preferences and ecology of this species. It apparently grew on rocky headlands, sea cliffs, coastal rocks and beaches (Kirk 1891, 1899; Cockayne 1921), and some herbarium specimens state that it also grew on sandy and gravel beaches at the high tide mark (e.g., WELT SP030104, SP030107). The species evidently had a most remarkable appearance when fresh, Cockayne (1921) noting that 'in appearance Lepidium obtusatum represents, even when in flower, a huge crusty saxifrage. Its leaves arranged in rosettes are very thick, glossy and rather dark green’. Its thick, fleshy leaves may have the been the basis for a vernacular name 'sea kale lepidium’ recorded by J. H. MacMahon (see WELT SP081926).

Conservation Status.

It is a matter of some irony that when it was described, Kirk (1891) stated, 'happily for Lepidium obtusatum ,it grows in a few spots which are inaccessible to sheep, so that it will probably hold its ground for many years’. This prediction did not come to pass; the species was first treated as 'Presumed Extinct’ by Williams and Given (1981), a status that has been maintained in all subsequent threatened indigenous vascular plant listings to the present (see Cameron et al. 1993; de Lange et al. 2009). The factors leading to the demise of Lepidium obtusatum are well documented ( Cockayne 1921; Norton et al. 1994; de Lange 2005). The species was a narrow-range endemic whose location on the margin of an actively expanding city meant that it was extremely vulnerable to habitat destruction (see de Lange 2005; de Lange et al. 2010a; de Lange et al. 2010c). Nevertheless it seems that, at least initially, it was very common within the small area it occupied, and Cockayne (1921) mentioned that the quarrying of rock from its cliff habitat, had, temporarily at least, caused an expansion in the population through the spread of 'underground stems’. Nevertheless, by 1951 it had gone extinct. From available evidence it seems that the biggest factor was not habitat loss but over collection ( Norton et al. 1994). Herbarium specimens show that following its formal recognition by Kirk (1891), it was repeatedly gathered by botanists who made copious collections (often gathering whole plants). Most of these gatherings occurred between 1900 and 1939 (and they intensified between 1920 and 1939) ending with the last known collection in 1951 ( de Lange 2005). During this period it is also likely that the modification of most of its habitat for housing and defense structures associated with military operations at Fort Dorset would have impacted on the population, as would the spread of weeds, especially those derived from nearby urban gardens. Today, all of the former range of Lepidium obtusatum is now choked in a rank growth of weeds, most especially veldt grass ( Ehrharta erecta Lam.).

Hybridism.

A suite of specimens (WELT SP081927A, B, C, J. H. MacMahon s.n., 1931, Seatoun) are tentatively identified here as a putative natural hybrid between Lepidium obtusatum and Lepidium oleraceum . These specimens, which appear to be pieces split from the same plant seem to have had an erect, shrubby growth habit, with somewhat woody, flexuous branches, while the basal and upper cauline leaves are narrowly elliptic to lanceolate, deeply and sharply incised to weakly pinnatifid. The flowers, though in poor order, have four stamens (pollen stainability 0%). Only a few silicles in the specimens are mature and these measure up to 4.05 × 2.75 mm, are suborbicular to ovate, narrowly winged, with the apex weakly notched. Significantly, they contain no seeds. The putative parentage is based on the knowledge that both Lepidium obtusatum (see collections cited above) and Lepidium oleraceum were sympatric at Seatoun (WELT SP09712, W. R. B. Oliver s.n.) and that no other Lepidium species was known to be present in that area at that time. The erect, shrubby growth habit is a feature of Lepidium oleraceum , while morphologically the silicles are a close match for Lepidium obtusatum . The shape of the cauline leaves fits within the range seen in Lepidium oleraceum , though their degree of dentition also approaches that seen in Lepidium amissum , Lepidium banksii and Lepidium panniforme .

Figures

Figure 16. Holotype of Lepidium amissum de Lange et Heenan.

Figure 20. Mature silicle of Lepidium amissum. AK 4473. Scale bar = 1 mm.

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

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

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

Figure 64. Holotype of Lepidium obtusatum Kirk.

Figure 65. Portion of Lepidium obtusatum showing rhizomatous growth and rosette leaves.

Figure 66. (From left to right) rosette, basal-, mid- and upper-stem leaves of Lepidium obtusatum. Scale bar = 20 mm.

Figure 67. Upper stem leaves of Lepidium obtusatum. AK 4476.

Figure 68. Mature silicle of Lepidium obtusatum. CHR 464564. Scale bar = 1 mm.