Callitriche petriei Mason 1959

17. Callitriche petriei Mason (1959: 315).

Type: — NEW ZEALAND. NORTH ISLAND. Ngaruawahia, Waikato R., 4 February1906, Petrie, D. s.n. (Holotype: WELT51443, isotype WELT51444).

Description: —Stem and leaf scales present. Leaf bases connate. Lingulate leaves, parallel-sided, 0.6–0.7 mm long × 5.7–6.8 mm wide, expanded submerged or floating leaves elliptic, 0.5–1.2 mm long × 1.5–2 mm wide, 3-veined; petiole 1.2–1.4 mm long; leaves of terrestrial plants broadly ovate, 1.2–1.4 mm long × 1.5–2.0 mm wide, petiole 0.5–1.2 mm long. Dioecious, flowers solitary, usually in one of a pair of axils on alternate sides of the stem. Bracts lacking. Styles erect, ± persistent, 1.7–2.2 mm long. Filament erect, 2.2–4.9 mm long; anthers 0.4 mm long × 0.5 mm wide, number of loculae unknown; pollen yellow. Fruit not strumose, subsessile or on pedicel to 0.5 mm, wider than high, greyish-brown when mature, 0.6–0.7 mm long × 0.7–0.9 mm wide, unwinged.

Illustrations: — Mason 1959, Fig. 10g.

Recognition: — C. petriei is the only Callitriche which is dioecious, however a number of other species appear to initially only produce female flowers and it may be necessary to be cautious in recognising plants based on this character unless they have very abundant flowers. The unwinged pale or golden-brown fruit will distinguish this species from all other Callitriche species in the region apart from C. chathamensis from which it can be distinguished by the smaller fruit.

Distribution: —Native. C. petriei is endemic to New Zealand, where it occurs on North and South Islands (Fig. 15a). On the North Island, it is scarce north of Auckland according to Mason (1959).

Habitats and Ecology: — Callitriche petriei occurs on damp mud and soil, in lake margin turf communities, on the margins of lakes and streams, in swamps and temporary pools, as well as occasionally in standing water of ponds and lakes, where it may grow permanently submerged (Mason 1959, Johnson and Rogers 2003). It is frequent in lowland indigenous riparian forest dominated by Dacrycarpus dacrydioides (P. de Lange pers. comm.) and can tolerate shade from non-native Salix species. It has been recorded with species such as Eleocharis acuta R.Br. (1810: 224), Galium palustre M.Bieb. (1808: 103), Hydrocotyle sulcata C.J.Webb & P.N.Johnson (1982: 165), Lobelia angulata G.Forst. (1786: 58), Myriophyllum propinquum A.Cunn. (1839: 30), Nertera depressa Gaertn. (1788: 124–125), Dacrycarpus dacrydioides, Persicaria strigosa (R.Br.) H. Gross (1913: 308), Potamogeton ochreatus Raoul (1844: 117) and Viola lyallii Hook. f., (1864: 16). 15–150 m elevation.

Conservation Status: — Callitriche petriei is classed as Least Concern (IUCN 2012) as it is widespread with stable populations and does not face any major threats. It is classed as Not Threatened in New Zealand (de Lange et al. 2018).

Notes: — Callitriche petriei was combined with C. chathamensis by Mason (1959), however differences between the two, such as the monoecy, larger fruit and larger leaves of C. chathamensis are significant, and justify their recognition as separate species.

The information presented here is based on a very small number of specimens bearing fruit. Most material in herbaria is not flowering and whilst the habit can be distinctive (see Fig. 15b), there is a need for information to be collected based on fruiting and therefore rigorously confirmed, material.

Selected specimens examined: — NEW ZEALAND: Tinamea Saddle, 6 February 1961, M.J.A. Simpson 2582 & J.B. Moss (CHR 521063); 25 November 1970, R. Mason & A.E. Esler 11473 (CHR 214376). NORTH ISLAND. Lake Moumahaki, Wanganui, 22 January 1989, C.C. Ogle 1762 (CHR 464160), Lake Waikato, Taranaki: R22 630 513, Wellington Land District, 10 March 2013, C.C. Ogle 6182 (CHR 625889); Lake Waikari, 10 December 1958, R. Mason & N.T. No. 6911 (CHR 111315); Huntly, 25 November 1958, R. Mason & N.T. Moar 6330 (CHR 109500); Lake Whangape, 15 m, 14 January 1990, P.J. de Lange 178 (CHR 466165); Paiko River, Patetonga, s.d., R. Mason 7463 (CHR 113280); Paiko River Patetonga, s.d., R. Mason 7464 (CHR 113281); Lake Alice, 16 March 1956, R. Mason 4090 (AD 108590, NSW! 935590); Roto Aira, February 1875, S. Berggren s.n. (G); Totara Reserve, Pohangina V., October 1973, [name illegible] (CHR 262315); Mangamahu, Wanganui, 16 October 1990, C.C. Ogle 2036 (CHR 471380). SOUTH ISLAND. Lake Heron, Ashburton Co., Canterbury, 27 March 1962, R. Mason 9374/1 (ANSP, PH); Riversdale, Mataura River S160/577760, 25 February 1973, R. Mason & E.M. Chapman 12788 (CHR 243613); Otamita Stream Mandeville SI69 74-51-, 27 September 1973, R. Mason & E.M. Chapman 12825 (CHR 243649); Lake Poteriteri, 55 m alt., 46° 4’ S, 167° 6’ E, s.d., M.D. de Winton s.n. (CHR 502290); Peel Forest, Canterbury, 13 February 1984, B.P.J. Molloy & A.P. Druce s.n. (CHR 607421).