Wardia hygrometrica

Harv. & Hook.

Family : Wardiaceae
Common names : Ward's moss

Wardia hygrometrica.photo j Sleath
© Jonathan Sleath

Wardia hygrometrica is an aquatic moss restricted to the mountains of the southwestern Cape. It belongs to the Wardiaceae, the only endemic moss family in South Africa.

This moss forms small to large, yellow-green or usually blackish green mats on rock in streams. The stems are 15–80 mm long, naked and black below when old, branching irregularly above the basal part (stipe). The leaves are evenly spaced, spreading to erect-appressed when dry, variable in shape and length, broadly elliptical and up to 2.2 mm long. The leaf cells are narrow and thick-walled. The midrib of the leaf is extremely variable: absent, present only in the leaf base, discontinuous and present only at the apex and base, or strong throughout. The cells at the basal margins of the leaf (alar cells) are strongly differentiated, enlarged and inflated, hyaline to yellowish.

Leaf under microsope

Plants are frequently fruiting (with sporophytes). The short (4–6 mm long), thick stalk or seta is twisted clockwise when dry and bears a pear-shaped capsule that contains the spores. The capsule is erect, short-cylindrical, smooth but somewhat ribbed when young and dry and stomata are absent. The lid of the capsule is long-beaked and remains attached to the central sterile tissue (columella) after the capsule has opened. The peristome (fringe of pointed teeth surrounding the opening of moss capsule) at the mouth of the capsule is absent or variously developed, with up to 32 short, blunt teeth. The spores are rounded, granulate and mostly 25–31 µm in diameter.

SEM image of Capsule

Conservation status
Although Wardia hygrometrica is restricted to the southwestern Cape, it is regularly seen and occurs in several protected areas e.g. Table Mountain National Park, Jonkershoek Nature Reserve and the Winterhoek and Cederberg Wilderness Areas. It is therefore not of conservation concern.

Distribution and habitat
Wardia hygrometrica is endemic to South Africa. Its distribution is centred in the mountains of the southwestern Cape, from the Cape Peninsula and Hermanus in the south, to the Cederberg in the north. A single locality is known from the mountains near Knysna.

It grows on rock, submerged or in splash-zones of fast-flowing mountain streams and waterfalls.

Derivation of name and historical aspects
According to the original description (Hooker 1837), Wardia hygrometrica was first collected by William Henry Harvey (1811–1866), a major contributor to South African botany. He discovered this remarkable moss ‘on the stony bed of a small mountain rivulet, at Paradise, on the eastern side of Table Mountain, Cape of Good Hope'. No date is given but it must have been after 17 September 2020, the date of his first arrival at the Cape (Glen & Germishuizen 2010).

The genus was named in honour of Nathaniel Bagshaw Ward (1791–1868), an English doctor with an interest in botany, with whom Harvey exchanged living plants. The specific epithet hygrometrica refers to the hygroscopic nature of the seta (stalk).

Wardia hygrometrica is characterised by its aquatic habitat, blackish stems, enlarged and coloured alar cells, persistent lid and short, blunt teeth at the capsule mouth. It is usually accommodated in its own family, the Wardiaceae, which is the only endemic moss family in South Africa. It has often been placed near the Fontinalaceae, another aquatic moss family. However, molecular data suggest that it is closely related to taxa in the Dicranaceae (La Farge et al . 2002).

The rigid, wire-like stem, straight, evenly spaced leaves and strong, broad midrib (when present) are morphological characters Wardia hygrometrica share with other aquatic mosses. Gametophytic (the plant body that produces gametes) variability is another characteristic of aquatic mosses and Wardia displays considerable variation in stem length and firmness, development of the stipe, leaf shape and length, midrib development and peristome morphology.

The short, stout stalk and absence of stomata on the sporophyte (the diploid plant form that produces spores) of Wardia hygrometrica are further adaptations to the aquatic habitat. The lid remains attached to the columella after the capsule has opened, which may assist in spore discharge.

Uses and cultural aspects
Records of local uses of this moss are lacking.

Growing Wardia hygrometrica

Wardia hygrometrica has very specific habitat requirements and will be difficult to cultivate.

References and further reading

  • Glen, H.F. & Germishuizen, G. (compilers) 2010. Botanical exploration of southern Africa, 2nd ed. Strelitzia 26. South African National Biodiversity Institute, Pretoria.
  • Hedderson, T.A., Cox, C.J. & Gibbings, J.G. 1999. Phylogenetic relationships of the Wardiaceae (Musci); evidence from 18s rRNA and rps4 gene sequences. The Bryologist 102(1): 26–31.
  • Hooker, W.J. 1837. Wardia : a new genus of mosses, discovered in southern Africa. Companion to the Botanical Magazine 2: 183–184.
  • La Farge, C., Shaw, A.J. & Vitt, D.H. 2002. The circumscription of the Dicranaceae (Bryopsida) based on the chloroplast regions trnL - trnF and rps4 . SystematicBotany 27: 435–452.
  • Magill, R.E. & Van Rooy, J. 1998. Flora of Southern Africa. Part 1 Musci, Fascicle 3 Erpodiaceae–Hookeriaceae . National Botanical Institute, Pretoria.


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