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Nature in Wales


Vol. 3, no. 2 Summer 1957

Poa Pratensis subspecies Subaerulea, in north Glamorgan and south Brecon

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(4) Waste places and walls Plants have been found grow-
ing on walls at Bwllfa, N. Glam., and Penderyn, S. Brecon. Sub-
caerulea has also been repeatedly found about the bases of tips of
colliery waste, where loose weathered shale is ideal for the spread
and development of long rhizomes and the conditions are somewhat
similar to the sand-dune environment. Other habitats include the
ballast between railway tracks, and moist roadside gutters, and
point to the widespread occurrence of the subspecies.
The area surveyed is bounded approximately on the south by
the Rhondda-fawr and on the north by the limestone outcrop in the
vicinity of Penderyn, S. Brecon. The soils are variable, but are
predominantly Glacial drift on the lowland areas, with poor
drainage and acid characteristics. The higher ground, approx-
imately above 700 ft., has soil of a more sedentary origin, though
peat development may occur locally. On these elevated areas
stations have been recorded on the Pennant Sandstone, Coal
Measures, Millstone Grit, Garb. Limestone and Old Red Sandstone.
The rainfall of the area is high, with an annual average between
1942-1951 of 61-2 in. at the Nanthir Reservoir, near Aberdare.
The following centres at which subcaerulea was recorded in-
dicate the area that the survey covered
N. Glamorgan Pen Rhys, Rhondda Treherbert
Craig Mountain, nr. Aberdare Cwmdare, nr. Aberdare
Bwllfa, nr. Aberdare Mynydd Cefh-y-Gyngon, nr.
Aberdare; Hirwaun; Craig-y-Llyn; Merthyr; Cilfynydd.
S. Breconshire Foel, Penderyn Pontpren, Penderyn
Cwm Cadlan Hepste Valley Ty Newydd, nr. Hirwaun.
The data collected for the populations actually measured is
presented in Table 1. The panicles were characteristically short,
2-branched at the nodes, and with acuminate glumes with 3 nerves
each. The number of spikelets per panicle is also rather low,
23-33 per panicle, and a bulk sample of spikelets gave 3-4 ±
0·08 florets/spikelet. The height of the culms was never very great,
and in most populations the straw was very short, though this
seemed to be much influenced by the environmental conditions.
The length of the culm internodes increases rapidly up the culm so
that the uppermost internode is longest, as is usually found in the
The vegetative features of the subspecies are characterised by a
loose tillering, resulting from a low rate of tillering at rhizome
nodes, though on sheep shelters much denser tillering was found,
presumably on account of trampling and close grazing. The sterile
tillers had several green leaves, and the number recorded at Wind-
ber, Bwllfa, was 3.9 ± 0-13 (Aug.) O(Dec) and 148 ± 0-12 (March)
Whilst fine hairs were invariably found at the junction of leaf blade
and sheath, the actual length and width of leaves varied within
single tillers of plants and between plants. Thus from two specimens
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