Callitriche chathamensis (Mason) Lansdown, 2022

Lansdown, Richard V., 2022, The genus Callitriche (Plantaginaceae, Callitricheae) in Australasia and Oceania, Phytotaxa 547 (3), pp. 243-284 : 253-254

6. Callitriche chathamensis (Mason) Lansdown comb. and stat. nov.

≡ Callitriche petriei subsp. chathamensis Mason (1959:317) .

Type: — NEW ZEALAND. CHATHAM ISLANDS. Tupuangi Lagoon, Pitt. I., Chatham Is., 1 February 1957, B. G Hamlin. 692 (Holotype: WELT SP003332, isotype CHR 121104) .

Description: —Stem and axillary scales present. Leaf bases connate. Lingulate leaves slightly wider toward apex, 1.0– 1.4 mm long × 8.0– 9.7 mm wide; expanded submerged or floating leaves ovate-elliptic 2.2–4.1 mm long × 0.8–2.5 mm wide, venation complex with frequent branches arising within and outside the secondary veins, secondary veins sometimes undulating, petiole 1.6–4.5 mm long; leaves of terrestrial plants unknown. Monoecious, flowers solitary, often alternating ♀ and ♂ along stem. Bracts lacking. Styles erect, 1.1–2.3 mm long. Filament erect, 4.5–6.8 mm long; anthers 0.5–0.6 mm long × 0.5–0.6 mm wide, quadrilocular; pollen yellow. Fruit not strumose, subsessile, wider than high, pale brown when mature, 0.6–0.9 mm long × 0.7–1.1 mm long wide, unwinged.

Illustrations: — Figure 4A (h) in Mason (1959). Fig. 1f .

Recognition: — C. chathamensis can be distinguished from all Callitriche species in the region by the pale or golden brown unwinged fruit which are wider than high, combined with the lack of bracts and the presence of both ♀ and ♂ flowers on the same plant.

Distribution: —Native. Callitriche chathamensis is endemic to the Chatham Islands east of mainland New Zealand, where it occurs throughout Rekohu (Chatham Island) and Rangihaute (Pitt Island) ( Champion and Clayton 2004), as well as on Mang’re (Mangare) and Hokorereoro (South East Island) (P. de Lange pers. comm.) ( Fig. 6 ).

Habitats and Ecology: — Callitriche chathamensis occurs on bare peat and mud on wet, peaty ground, commonly at the edges of streams and lakes, and on steep cliff faces, ledges and rubble near the sea. It was described as occurring in a turf community in shallow water in lakes characterized by Chara globularis Thuiller (1799: 472) , Lilaeopsis novae-zelandiae A.W. Hill (1927: 549) , Myriophyllum triphyllum Orchard (1979: 259) , Nitella hyalina (De Candolle) C. Agardh (1824: 126) and Ruppia polycarpa R. Mason (1967: 524) with a range of other species, including Limosella australis R. Br. (1810: 443) , Myriophyllum pedunculatum subsp. novae-zelandiae Orchard (1979: 274) , Potamogeton cheesemanii A.Benn. (1883: 66) and Triglochin striata Ruiz & Pav. (1802: 72) ( Champion and Clayton 2004). There is no information available on the elevation range of this species, but the maximum elevation on the islands is 299 m.

Notes: — Mason (1959: 317) combined C. chathamensis as a subspecies under C. petriei , however this combination is difficult to maintain as the differences between these two taxa are much greater than those between many other Callitriche species. The most significant difference is that C. petriei is dioecious, which is otherwise unknown in the genus. In addition, both the linear and expanded leaves of C. chathamensis are typically larger than those of C. petriei and often show complex venation, in contrast to the simple venation of C. petriei . The filament and anther may be larger in C. chathamensis and the fruits are typically larger. These differences are more than adequate to justify recognition of these as two separate species.

The information presented here is based on a very small sample size, such that individual specimens show characters which differ from the majority of measurements. For example, on Courtney s.n. (CHR 436463), all flowers are female and immature, which suggests that female flowers develop first followed by male flowers (as appears to be the case with C. cyclocarpa ). It is clear that, as with so many of the Callitriche species native to the region, there is a need for extensive research into morphological variation based on living material.

Conservation Status: —Native. Callitriche chathamensis is endemic to the Chatham Islands, New Zealand, where it occupies a limited geographic area with an Area of Occupancy (AOO) estimated at less than 4 km 2. Due to the inherent vulnerability caused by this limited geographic range and possible real threat from alien plants, this subspecies is assessed as Vulnerable D2 ( IUCN 2012). It is classed as Naturally Uncommon, Island Endemic, Range Restricted, Sparse ( de Lange et al. 2018).

Selected specimens examined: — NEW ZEALAND: CHATHAM ISLANDS. 1872, H. H. Travers s.n. ( MEL) ; Chatham Island, Waitangi, 1901, L. Cockayne & F. A. D. Cox 1480 ( WELT SP051433, WELT SP003299) ; South East Island, December 1961, B. Bell s.n. ( CHR 158307 ) ; Chatham Island, Lake Te Roto, 20 m, 27 February 2003, P. D. Champion CH 2403 ( CHR 568034 ) ; South East Island (Rangatira), Watercress Bay, 26 February 1986, S. Courtney s.n. ( CHR 436463 ) .

Figures

FIGURE 1. Fruits of Callitriche in Oceania and Australasia: a—C. antarctica, b—C. aucklandica, c—C. brachycarpa, d—C. brutia, e—C. capricorni, f—C. chathamensis, g—C. cyclocarpa i face on and ii end on, h—C. cycloptera, i—C. deflexa, j—C. fuliginea.

FIGURE 4. The distribution of specimens of C. brutia in Oceania and Australasia based on records held by AVH.

FIGURE 6. The distribution of C. chathamensis based on records held by AVH, supplemented by P. de Lange (pers. comm.)