Cardamine cubita Molloy, Heenan et Smissen, 2013

Heenan, P. B., Molloy, B. P. J. & Smissen, R. D., 2013, Cardamine cubita (Brassicaceae), a new species from New Zealand with a remarkable reduction in floral parts, Phytotaxa 140 (1), pp. 43-50 : 48-49

Cardamine cubita Molloy, Heenan et Smissen , sp. nov. ( Fig. 1 )

Cardamine cubita is distinguished from all other New Zealand indigenous Cardamine spp. by its minuscule size, cotyledons present when flowering and fruiting, apetalous flowers, two stamens, filaments distally bent, and one ovule in each carpel.

Type: — NEW ZEALAND. North Canterbury, Lees Valley, wetland on floodplain of the Ashley River and its tributary streams, ca. 400 m a.s.l., 45°9’S; 172°11’E, B. P. J . Molloy s.n., 2 March 2013 (holotype CHR 612054 ) .

Annual herb, 3.0– 5.5 mm across, single stem, not branched; stems glabrous. Cotyledons persistent, opposite, lamina 1.4–1.9 × 1.5–2.1 mm, pinkish-purple, orbicular, apex retuse; petiole 0.7–0.8 mm long, pinkish. Leaves up to 2.2 mm long, simple or 1-pinnate; lamina green to purple-green, membranous, sparsely hairy on adaxial surface, glabrous on abaxial surface; hairs 0.2–0.25 mm long, spreading to patent, 1–2-septate; petiole 0.6–0.8 mm long; terminal pinna 0.8–1.2 × 1.3–1.4 mm, simple, broadly orbicular, margins entire or shallowly 1–2-lobed, lobes with hydathodes, apex subacute to obtuse, usually with a distinct hydathode, base truncate to cordate; lateral pinnae absent or 1–2, 0.2–0.3 × 0.2–0.3 mm, petiolule indistinct. Inflorescence single, racemose, racemes 1–2-flowered, flower 0.8–0.9 mm diam.; peduncle up to 1.4 mm long, ca. 0.3 mm diam. at base, erect to ascending, glabrous. Pedicels ca. 1.1 mm long, ca. 0.2 mm diam., spreading to ascending, glabrous. Sepals 0.6–0.7 × 0.4–0.45 mm, elliptic-oblong, saccate, green or red-brown, glabrous, margin white and membranous, apex obtuse, base truncate; black-brown gland on adaxial surface of one sepal. Petals absent. Stamens 2; filaments 0.36–0.4 mm long, 0.06 mm diam., conspicuously bent 90° distally; anthers ca. 0.14 mm long, cream to pale yellow, when dehiscent held slightly below the stigma. Ovary 0.5– 0.55 mm long, 0.2–0.22 mm diam., ± terete, green, glabrous; ovules 2; style ca. 0.03 mm long, ± terete; stigma ca. 0.14 mm diam., white. Siliques ca. 4.0 × ca. 0.8 mm, glabrous, beak ca. 0.6 mm long, septum central vein absent; replum ca. 0.3 mm wide, flattened. Seeds ca. 0.8 mm long, ca. 0.55 mm wide, short-oblong, brown.

Recognition:— Cardamine cubita is readily distinguished from all other indigenous and naturalised species in New Zealand by the diminutive size of its vegetative and floral parts, cotyledons present when flowering and fruiting, apetalous flowers, two stamens, filaments that are distally bent 90°, carpels each with one ovule/seed, and fruit being 4 mm long.

Distribution and habitat:—Known from a single locality near the upper Ashley River in Lees Valley, North Canterbury, New Zealand. C. cubita covers an area of about 20 m 2 of an extensive wetland with varying degrees of natural drainage, disturbance (including artificial drains), and plant composition. Surface and buried wood of Phyllocladus alpinus Hooker (1853: 235) is widespread throughout indicating that this shrubby conifer at one time dominated the wetland. At present this site is highly modified and occupied by grasses, sedges, rushes, and herbs, both indigenous and naturalised. Within this area C. cubita occurs in a short turfy micro-habitat over a peaty soil 1–2 m deep. Associated plants include Spiranthes novae-zelandiae , Eleocharis gracilis Brown (1810: 224) , Lobelia angulata Forster (1786: 58) , Ranunculus glabrifolius Hooker (1834: 243) , Gonocarpus micranthus Thunberg (1783: 55) , Chaerophyllum colensoi var. delicatulum ( Allan 1961: 461, 973) Chung (2007: 678), Nertera balfouriana Cockayne (1912: 50) , Centrolepis ciliata ( Hooker 1844: 85) Druce (1917: 614) , Drosera arcturi Hooker (1834: 247) , Epilobium komarovianum Léveillé (1908: 98) , and Sphagnum cristatum Hampe (1874: 661) . The entire site supports a wide range of primary and secondary habitats with a rich and varied wetland flora that would repay further investigation.

Conservation status:—Using the New Zealand threat classification system, C. cubita qualifies as ‘Threatened/Nationally Critical’ ( 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 are added the qualifiers Data Poor (because accurate data on the total number of individuals and trend data are not available) and One Location. Further field survey is needed to determine the distributional range and the number of individuals.

Species epithet:—The epithet cubita (elbow) refers to the distally bent filaments of this species ( Fig. 1F ).

Figures

FIGURE 1. Cardamine cubita. A. Flowering plant with large cotyledons and smaller adult leaves. B. Fruiting plant. C. Hair on leaf adaxial surface. D–F. Flowers with two stamens distinctly bent near apex. G–I. Fruiting siliquae. Scale bars: A, B, G, H = 1 mm; C = 0.1 mm; D, E, F, I = 0.5 mm.