Callitriche aucklandica Mason 1959

2. Callitriche aucklandica Mason (1959: 307).

Type: — NEW ZEALAND. AUCKLAND ISLANDS. Auckland I., J.B. Hair s.n., Nov. 1954. (Holotype: CHR 89341, isotypes: CHR 89342!, CHR 89344!).

Description: —Stem and leaf scales present. Leaf bases connate. Lingulate leaves unknown; expanded submerged or floating leaves unknown; leaves of terrestrial plants slightly fleshy 3.7–8.0 mm long × 1.2–4.0 mm wide, 3-nerved, occasionally with short free veins, blade and petiole poorly differentiated. Flowers solitary or sometimes ♂ and ♀ together. Bracts caducous, 0.3 mm long. Styles persistent, erect, 2.0– 2.5 mm long. Filament erect, <9 mm long; anthers, 0.6–0.8 mm long × 0.5–0.8 mm wide, number of locules unknown; pollen yellow. Fruit not strumose, subsessile, wider than high, dark brown, 1.1 mm long × 1.2–1.3 mm wide, narrowly winged throughout.

Illustrations: — Figures 7 (a–b) and 7A(a–b) in Mason 1959. Fig. 1b.

Recognition: — C. aucklandica can be distinguished from all other Callitriche species except C. antarctica by the fleshy leaves with connate bases. C. aucklandica differs from C. antarctica in the narrow wing on the fruit.

Distribution: —Native. Callitriche aucklandica is endemic to the Auckland Islands, where it has been recorded from Dundas Island (Falla et al. 1979), Ewing Island and Auckland Island but its occurrence on the other islands cannot be discounted.

Habitats and Ecology: — C. aucklandica is described as common in wet ground at low altitude (Johnson and Campbell 1975), it occurs in coastal to montane areas on exposed ground, in pools and on sodden peat, in heavy shade under both young and mature Olearia Moench (1802: 254) forest, as well as in Metrosideros umbellata Cavanilles (1797: 20) mixed forest and with Stellaria media (von Linné) Vill. (1789: 615) between Poa foliosa tussocks (Falla et al. 1979, Johnson and Campbell 1975, Webb et al. 1988, Lee et al. 1991). It often occurs near bird colonies and in areas recovering after use by sea lions but also on exposed mud within forest and scrub (Johnson and Campbell 1975). There is no information available on the elevation range of this species, but the maximum elevation in the Auckland Islands is 705 m.

Notes: —There is, as yet, no confirmation that C. antarctica occurs on the Auckland Islands (see above). If C. antarctica is confirmed from the islands then it is possible that information on C. aucklandica may need to be revised as many identifications in the literature and on herbarium specimens appear to have been based on the assumption that C. aucklandica is the only Callitriche species represented on the Auckland Islands.

Conservation Status: — Callitriche aucklandica is endemic to the Auckland Islands in New Zealand, where it occupies a limited geographic area on three islands, each of which is treated as a single location (IUCN 2012). Due to the inherent vulnerability caused by this limited geographic range and possible real threat from factors such as alien plants and climate change, this subspecies is assessed as Vulnerable D2 (IUCN 2012). In New Zealand, it is classed as Naturally Uncommon, Island Endemic, Range Restricted, Sparse (de Lange et al. 2018).

Additional material studied:— NEW ZEALAND: AUCKLAND ISLANDS. (P03304423); 1839–1843, J.D, Hooker s.n. (CANB277895); 1874, H. Krone s.n. (STU 15648); Musgrave Peninsula, 22 November 1943, W.H. Dawbin s.n. (CHR251989).