MOLINIA CAERULEA (L.) MOENCH SUBSP. ARUNDINACEA (SCHRANK) H. PAUL, A SUBSPECIES OF PURPLE MOOR-GRASS P. J. O .
This is an attractive Molinia and a good subspecies which is readily recognisable but seldom reported. Its taxonomic rank has been the subject of alteration and its synonomy includes Molinia litoralis Host, M. caerulea subsp. litoralis (Host) H. Paul and var. litoralis (Host) Griseb. The common subsp. caerulea is widespread in Britain on heath, moorland, scrub woodland rides, on mountain grass slopes and by lowland river sides. It is a very variable taxon and its height and length of leaves is no guidance in the determination of varieties. Very small plants of 8-12cm have been named var. pygmaea, but these are plants of stunted growth through sheep grazing. This subspecies occasionally attains 50cm in height, but this is unusual. Most plants of this taxon are seen in isolation and are seldom in competition with other plants. By contrast, subsp. arundinacea is a tall plant, strong and with the ability to make good growth in shade and in dense competition. The stems are mostly over 100cm; Conert (1961) gives 120-150cm and Tutin (1980) up to 250cm. It has comparatively flat leaves of 30-80cm in length and with a slight curl at the edge. The leaf width is variable. I find it 5-7-5mm but Conert (1961) gives a width up to 12mm; this can be compared with the width of l - 6 m m for subsp. caerulea. A comparison of the length of the spikelet and the lemma cannot be used to separate the two subspecies. The outstanding feature of difference in the subsp. arundinacea is the length of the panicle, for which Conert (1961) gives 30-50cm, but I have taken specimens with a panicle of 65cm. This length is more than double that of the largest specimens found in the common subsp. caerulea, which I find seldom attains 30cm, although Hubbard (1968) gives up to 40cm. Unlike subsp. caerulea, this subspecies has a specific habitat. It is found in fens and fen river Valleys on light peat or on sand over peat and a fluctuating water level and a high winter level is essential. It is tolerant of considerable plant competition and shade. Its plant associates are tall, and include Cladium mariscus (Great Fen Sedge), Filipendula ulmaria (Meadowsweet), Juncus effusus (Soft Rush), J. subnodulosus (Blunt-flowered Rush) and Phragmites australis (Reed), often under young Salix (Willow) and Betula (Birch). In the dense ground cover beside a fen ride or ditch, subsp. arundinacea is difficult to see until you have recognised how this plant fits in with the competition. It does not grow erect and its long leaves and panicle lie over and through the Cladium and Filipendula and are largely hidden from view. T o release the panicle and leaves, move a stick into the Vegetation and note the arc of the panicle with its interrupted groups of branches, which are long and spreading. In Suffolk, this subspecies occurs at Pashford Poors Fen, Lakenheath, also in a small fen near the road at Lt. Eriswell Hall and on Palmers Heath near
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Suffolk Natural History, Vol. 22
Brandon, all in v.c. 26. In 1985,1 found it on Little and Middle Fens, South Lopham v.c. 27. Swann (1975) gives four stations for W. Norfolk v.c. 28. It is no doubt to be found elsewhere in East Anglia. National records are few and new reports would be of interest. References Conert, H . J. (1961). The Classification and anatomy of the Arundinae. Weinheim. Hubbard, C. E. (1968). Grosses. Harmondsworth. Swann, E. L. (1975). Supplement to the Flora of Norfolk. Norwich. Tutin, T. G. etal., eds. (1980). Flora Europaea, 5. Cambridge. P. J. O. Trist, Glovers, 28 High Street, Balsham, Cambridge CB1 6DJ
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Trist, P. J. O.