Perennials, c. 50–120 cm tall; rhizome ±horizontal, stout; stems densely tufted, ±hard (difficult to compress), shining, yellowish green, (0.6–) 1.3–2.5 (–3.0) mm in diam.; pith dense, of astericiform cells, irregularly interrupted with small ±circular to ellipsoid lacunae; ridges 22–65, ±distinct when dry; subepidermal sclerenchyma strands present; epidermis cells ±uniform in size. Cataphylls usually 3–4, with inner ones to 18 cm long, c. 1 cm wide, lax, abaxially yellow-brown to ±brown distally, dull or slightly glossy, dark glossy (reddish) brown at base, adaxially silvery golden (pale) brown. Lower bract erect, (6–) 10–18 (–21) cm long, much exceeding inflorescence; sheath not inflated, ±narrow. Inflorescence 2–6 cm long, diffuse, with densely clustered flowers; flowers 3–20 per subglobose cluster and (1–) 3–12 (–20) clusters per inflorescence. Tepals subequal, stramineous to greenish stramineous-brown, sometimes tinged red-brown; outer tepals slightly longer, acute, (1.7–) 2.1–2.5 (–2.6) mm long, with margins narrow; inner tepals acute to subobtuse, with broad membranous margins. Stamens 3; anthers c. 0.4–0.6 mm long; filaments c. 0.5–0.7 mm long; style 0.1–0.3 mm long; stigmas c. 0.5–1.0 mm long. Capsule ±trilocular to imperfectly so, narrowly oblong-ovoid to ellipsoid, c. 2 mm long, obtuse, minutely mucronate, golden brown to pale castaneous-brown, equalling or slightly shorter than perianth. Seeds pale brown, obliquely ellipsoid, apiculate, 0.4–0.5 (–0.6) × c. 0.2–0.25 mm, c. 12–16-striate, reticulate; appendages absent.
Pith very finely interrupted with minute lacunae; Capsule trilocular.
Known from New Zealand, Stewart Is., Chatham Is. and Kermadec Is., temporary introduction reported from England. In the literature often referred to as J. gregiflorus. 10: grb. 51: CTM, KER, NZN, NZS.
10. GREAT BRITAIN: Wyboston, Eaton, 11 Jul 1948, Dony (K).
51. CHATHAM IS.: Chatham Islands, Apr 1967, Burke (WELTU). KERMADEC IS.: Raoul Is., Blue Lake, W.R.Sykes 1222K (CHR). NEW ZEALAND NORTH: Northland, Awanui, L.A.S.Johnson 7499 (CHR, NSW, PRA); Manukau Co., ESE of Clevedon, A.E.Orchard (AK, K, NSW); Bunnythorpe, 6 Mar 1930, V.D.Zotov s.n. (CHR, NSW). NEW ZEALAND SOUTH: Lincoln, E.Edgar 18 (CHR, NSW); Onehunga, A.Sinclair 803 (NSW, PRA); Lake Wanaka, Glenhu Bay, 11 Feb 1966, B.G.Briggs (CHR, NSW).
Damp, usually disturbed open sites, pastures, margins of swamps, from sea level to c. 1000 m.
Juncus edgariae is similar to J. gregiflorus of Australia and J. durus of New Guinea. It differs from both in having a more conspicuous stem striation and narrower capsule shape. While J. edgariae has pith lacunae small, usually circular to ellipsoid, J. durus is characterized by elongated, large lacunae, and J. gregiflorus has pith reduced to septa-like plates.