Photo
by Dr M Lueth ©.
*1: Near Marazion,
1897, LJC (BM) (Paton 1969a: 722, as Pottia
commutata).
*2: Near Wanson Mouth,
S. of Widemouth, 1961, JAP (BBSUK) (Paton
1969a: 723, as Pottia
starkeana subsp. conica).
A taxonomic review by Ros et al. (1996) concluded that
only spore morphology is useful in separating species in the
complex of variable forms comprising M. davallianum and M. starckeanum, which
D.F. Chamberlain (in Smith 1978) classified as Pottia starkeana (with
four intraspecific taxa) and P. commutata. They
emphasised that they 'found no correlation between the type of
peristome and any other sporophyte character. Taxonomic value
[of peristome]: none.' Blockeel & Long (1998) and Smith
(2004) followed this treatment so that the species would
include Cornish plants with the peristome well developed
(formerly treated as P. commutata) and others
with the peristome rudimentary or absent (formerly treated as
P. davalliana subsp. conica or P. starckeana subsp. conica). Both differ
from forms now treated as Microbryum starckeanum
in having spores with a regularly rounded outline and
papillose or spinose projections, rather than a warty outline
formed by fewer large projections (Ros et al. 1996). Hill et al. (2008: 149)
restored var. commutatum onto the
British list on the basis that forms with a long peristome
'are too distinctive to be subordinated completely to M. davallianum'.
However, they present no evidence of correlation of peristome
development with other characters that would contradict the
analysis by Ros et
al.
A gathering from Lizard (DTH
96-558) is intermediate between 'commutata' and 'conica', in combining
a well developed peristome (typical of commutata) with
spinose spores (which occur in conica, whereas commutata normally has
papillose spores). All of the rather few records of 'commutata' from
Cornwall are from sites within 100 m of the coast but a
minority of records of 'conica' are from much
further inland.
Grows as scattered plants or forming low lawns in
small or larger patches. Notes on habitats in C&S are as
follows. Occurs as colonist on exposed mainly or partly bare,
neutral to basic mineral soils. Most sites are free-draining
and rather dry or drought prone, often stony, and unshaded or
less often lightly shaded. Habitats include paths and soil
patches on cliff slopes, thin soil on top of old
mortared-stone wall, thin soil on top of 'hedge' above
sea-cliffs, clay-mud of old track, gravel path above cliffs,
bank beside path above sea-cliff, other earthy banks, edge of
coastal arable field, barley and stubble fields, slope of
reservoir dam, and base of wall of church. Associates recorded
were other small acrocarps, among them Barbula convoluta, B. unguiculata, Bryum dichotomum, Bryum ruderale, Fissidens incurvus, Microbryum rectum, Phascum cuspidatum
var.
cuspidatum,
Pseudocrossidium hornschuchianum.
Commonly c.fr. [only recorded with mature capsules
and ripe spores]: capsules immature 1, 6, 9, 11, 12; dehiscing
1, 3, [6], 11, 12, dehisced 3, 6,
11.