Parnassia palustris L., Grass-of-Parnassus
Account Summary
Native, frequent but local. Circumpolar boreo-temperate.
1882; Stewart, S.A.; Callow (or Carrick) Hill.
April to December.
Growth form and preferred habitats
In B & I, this somewhat tufted, hairless perennial with a short vertical rootstock and cordate, stalked leaves, bears lovely, solitary, pure white flowers and is a plant of three completely distinct habitats: wet dune-slacks, base-rich marshes and fens, and flushed areas of otherwise nutrient-poor organic soil on limestone hillsides or below limestone cliffs (An Irish Flora 1996; Bonnin et al. 2002). In Ireland, it is mainly found either at the coast, in species-rich wet hollows in fixed grey dunes, or else in damp to wet grassy ground around the upper basins of the larger limestone lakes of the W and the W Midlands. Elsewhere on the island, it is local and rather rare, including on limestone hillsides and below cliffs (An Irish Flora 1996). In all of these situations, seepage of ground water is almost invariably present and the vegetation types supported by the precise conditions in which P. palustris grows, possess a short, not too dense, nor very competitive plant cover.
While in overall terms we tend to think of P. palustris as a calcicole, or a weakly-calcicole species, it really is unusual in frequenting soils derived either from base-rich rocks (usually calcareous), or of moderately base-poor peat or leached clay character (Flora of Connemara and the Burren; Sinker et al. 1985; Grime et al. 1988, p. 170). In W Ireland, these two infertile and unproductive soil types overlap when P. palustris grows on sufficiently damp, percolated areas of cut-over acid peat bogs, or on shallow, raw humus, whenever these types of organic soils are formed directly overlying limestone rocks (Flora of Connemara and the Burren).
In Britain, P. palustris is generally considered to require an open, permanently moist site in marshy, peaty grasslands (both meadows and pastures) and in short sedge and grass fen margins around lakes and ditches. It is also found on more upland moorland sites, in flushes or in small damp hollows associated with base-rich rocks and peaty soils. The form of the plant with this mainly inland ecology is sometimes referred to as var. palustris. In coastal situations around B & I, P. palustris sometimes occurs as a genetically distinct dwarfed ecotype or ecodeme (var. condensata Travis & Wheldon) in the seasonally damp ground of dune-slacks and machair (Gornall 1988).
Ecological requirements for successful establishment
In all these various situations, seepage of ground water is almost invariably present and the vegetation that is supported by the precise conditions in which P. palustris grows, tends to possess a short and not too dense nor very competitive cover. A recent study has found that P. palustris possesses an arbuscular mycorrhizal partner, which must assist it in obtaining soil nutrients in competition with its neighbours (Eriksen et al. 2002).
A study in Scandinavia by Hultgard (1987) found that the species there is favoured by the existence of bare ground resulting from moderate levels of either natural or human-inspired disturbance (eg periodic flooding, mowing, grazing, trampling, or in roadside conditions and in quarry pits). In many of its Fermanagh damp grassland sites, the vegetation probably appears more closed than really is the case. The seed is tiny and very lightweight, so that bare ground and near zero competition (plus the presence of its mycorrhizal partner) are probably all essential for germination and successful establishment. Additional ecological requirements of P. palustris were identified as a fairly high level of oxygen supply at the roots, a need that is met by the often observed water movement in the soil it occupies, adequate mineral nutrition (ie just enough to avoid stimulating much plant competition for nutrients, light and space), a substrate which is not too acidic and illumination generally close to full sunlight (Hultgard 1987).
Genetic variation
P. palustris s.l. is a complex of several closely related races or cytodemes and has a wide circumpolar boreal-temperate distribution (Hultén 1971, Map 68). The species contains two principal cytodemes, a diploid (2n=18) and a tetraploid (2n=36), forms which are morphologically indistinguishable in B & I, the Netherlands and in Scandinavia (Gadella & Kliphuis 1968; Hultgard 1987; Wentworth & Gornall 1996). The tetraploid is very probably of autopolyploid origin and it occupies the more northerly portion of the species range, while the diploid appears to be more or less confined to the area south of the limit of the last glaciation (the Midlandian in Ireland and the Devensian in Britain) (Gornwall & Wentworth 1993).
Fermanagh occurrence
In Fermanagh, P. palustris has been recorded in 57 tetrads, 10.8% of those in the VC. It is distributed chiefly in wet fens around the shores of Lower Lough Erne and of smaller lakes, plus in flushed areas around limestone hills on the Western plateau. It also occurs more locally and less abundantly in the SE of the county on the shore of Upper Lough Erne, at Galloon Td, near the Crom estate and along the string of marl lakes that lie between Magheraveely and Rosslea in the extreme E of the county.
The fact that the distribution map contains eight tetrads with pre-1975 records only indicates there have been definite population losses across the VC. This is readily attributed to drainage operations and other changes in land use, including conifer plantation and agricultural grassland improvements.
Ecological indicator species
In Fermanagh, P. palustris has proved to be a good high- to late-summer flowering indicator species for such locally rare or scarce plants as Anagallis tenella (Bog Pimpernel), Dactylorhiza incarnata (Early Marsh-orchid), Eleocharis quinqueflora (Few-flowered Spike-rush), Eriophorum latifolium (Broad-leaved Cottongrass) and Saxifraga aizoides (Yellow Saxifrage). It is almost invariably accompanied by more common species of similar wide or 'bimodal' (ie tolerating two alternative environments) ecological amplitude, such as Briza media (Quaking-grass), Carex panicea (Carnation Sedge), Pinguicula vulgaris (Common Butterwort) and Triglochin palustre (Marsh Arrowgrass).
The bimodal nature of the environmental behaviour and habitat occurrence of P. palustris is reflected in the fact that in the Great Britain-based National Vegetation Classification, the species features in one form of mesotrophic grassland (MG2), two each of calcicole and calcifuge grasslands (CG9, CG14 & U15, U17) and in five mires (ie fens and bogs) (M8, M9, M10, M13 & M38) (Rodwell et al. 1991b, 1992).
Flowering reproduction
Grass of Parnassus blooms from July onwards but reaches its peak in August and September. The protandrous solitary, 15-35 mm diameter flower has pure white petals, decorated with conspicuous veins which may look white or greenish. Each flower possesses five sterile stamens or staminodes alternating with five functional ones. The staminodes become ± spathulate at their apex, each bearing 7-15 long, hair-like processes tipped with shining yellowish glands. These staminodes act both as nectaries and as pseudo-nectaries, attracting insect pollinators with their conspicuous glistening but non-rewarding globular tips, while each also produces nectar at its base. The main insect visitors are hoverflies and other Diptera, but the range of insect visitors can include ants, short-tongued bees, butterflies and moths (Proctor & Yeo 1973).
Experimental studies in Norway have shown that the presence of staminodes increases both the number and the duration of pollinator visits and thus they facilitate either cross-pollination or self-pollination, depending upon the particular population involved in the study (ie either coastal or alpine populations) (Sandvik & Totland 2003).
Selfed flowers produce a drastically reduced number of seeds, up to 95% fewer seeds per ovary than open-pollinated flowers. At the alpine level, the Norwegian workers found significantly more open-pollinated than emasculated flowers produced fruit in comparison with the same experiment at sea-level. Thus self-pollination aided by pollinators transferring pollen within the same flower, occurred more frequently than outcrossing at the alpine level, while in contrast, outcrossing was the norm at the lower altitude and here selfing was rare. Thus, although the flowers are protandrous, releasing their pollen before the stigma ripens, the degree of outcrossing varies substantially across the species distribution (Sandvik & Totland 2003).
Seed production, dispersal, survival and germination
The solitary, large, round, purple fruit capsule splits when ripe to release an approximate mean of 1,600-1,900 seed for dispersal on the breeze (Ridley 1930). Salisbury (1942) estimated that with a percentage germination rate of 76%, each plant had a reproductive capacity of around 1,300 potential offspring per annum. According to the soil seed bank survey of NW Europe, the seed is transient to short-term only (surviving less than one year (five studies), or 1-5 years (one study)) (Thompson et al. 1997).
Irish occurrence
The occurrence of P. palustris is typically very local throughout its Irish distribution, even when the plant is relatively frequent in an area. The presence of the plant is seldom abundant, although it does form rather diffuse, possibly clonal patches, in old managed grassland. It is very frequent in the W and west-centre of the island, but absent or very rare from the southern third of the country, while in the north it is scarce and mainly coastal (New Atlas).
British occurrence
P. palustris is local in much of Britain, but it is absent or very rare from S Wales and large areas of C & S England. There has been a long-term decline in the population of the diploid form, in particular in S England, most likely due to drainage operations over the last half century at least. The widespread distribution of the tetraploid form in the N & W of the British Isles seems to be very much more stable, although here also there is a definite westerly preponderance of the species (New Atlas).
European and world occurrence
P. palustris, on a worldwide basis, is a polymorphic collection of subspecies or species that is circumpolar in the boreo-temperate zone (Hultén & Fries 1986, Maps 1040 & 1041). P. palustris is widespread in Europe from Iceland and the whole of Scandinavia, to Denmark, the Netherlands and all of France except the NW. To the south, it stretches from N Spain and Morocco eastwards to Italy, the Balkans and Greece, although it is absent from the Mediterranean islands (Jalas et al. 1999, Map 3257). In the more northerly boreal areas, Hultén & Fries (1986) map a circumpolar subarctic-montane form they distinguish as subsp. neogaea (Fern.) Hult. (= P. obtusiflora Rupr.), although they admit its occurrence is imperfectly known.
Names
The genus name 'Parnassia' is a shortened form of the Latin name given by the 16th century Flemish herbal writer Mathias de l'Obel. He called the plant 'gramen Parnassi', a translation of the Greek 'agrostis en Parnasso', mentioned by the ancient writer Dioscorides (and hence the English common name, 'Grass of Parnassus', first translated into English by Lyte in 1578). It is called after the Greek mountain holy to Apollo and the Muses, where the species does indeed occur (Gilbert-Carter 1964; Strid 1986; Stearn 1992). Grigson (1987) supposes that the herbalist was inspired to make a connection to this prestigious religious location by the beauty of the prettily green-veined pure white flower, and to the current writer this does not appear too far-fetched, it being my favourite Irish wildflower.
It is, of course, somewhere between difficult and impossible to connect our P. palustris with the plant referred to by Dioscorides. According to the plant polymath David McClintock, de l'Obel included Maianthemum bifolium (May Lily) under gramen Parnassi, and the woodblock illustrations provided for Matthiolus in 1562 and thereafter (many editions in several European languages until 1604), or for Tabernaemontanus in 1590, are shown flowerless and indeed look quite like May Lily, or even like a broad-leaved pondweed (McClintock 1966, p. 199 & Plate 9). The flower was considered by these early botanists to resemble (or be) a white form of Hepatica noblis (ie H. alba) and, perhaps because of this, Gerard (1597), in his first edition, gave the species the medicinal properties of the latter for the treatment of liver disorders, calling it 'White Liverwort'. In the second much improved edition of 'Gerard's Herball' (1633) edited by Thomas Johnson, the latter corrected the illustration used, and also displayed a double-flowered form of the plant (p. 840), although Johnson continued to pronounce its supposed medicinal properties as a stomach remedy preventing vomiting and for helping to break and pass liver stones. Launert (1981) continues to illustrate and feature P. palustris as a medicinal plant to this day, although there is no mention of it in Grieve's monumental, comprehensive herbal (Grieve 1931).
The Latin specific epithet 'palustris' is a masculine form of the two words meaning swamp or bog, 'palus, udis', and refers to the damp ground in which the plant typically grows (Gilbert-Carter 1964). Other English common names include the prosaic and inaccurate 'White Buttercup' and the somewhat better 'Bog Star'. The species is grown in gardens, especially by alpine gardeners (Grey-Wilson 1989; Griffiths 1994).
Threats
Drainage of marshy ground and, elsewhere, excessive disturbance from grazing or trampling stock.
ROSACEAE – Rose family