Conservation of Britain's biodiversity: Hieracium cacuminum, Summit Hawkweed (Asteraceae)

Abstract

Hieracium cacuminum, Summit Hawkweed, is a rare endemic Welsh hawkweed which has been confused with H. siluriense. A review of the records and field work showed that 240 plants are known in three sites; it was not refound in three other sites. It occurs on Old Red Sandstone cliffs and rocks in the Brecon Beacons. It is 'Endangered' under the IUCN Threat Criteria.

Full text

463
HIERACIUM CACUMINUM
Watsonia 26: 463–468 (2007)
Conservation of Britain’s biodiversity: Hieracium cacuminum,
Summit Hawkweed (Asteraceae)
T. C. G. RICH*
Department of Biodiversity and Systematic Biology, National Museum of Wales,
Cardiff CF10 3NP
and
P. A. SMITH
128 Llancayo Street, Bargoed, Mid Glamorgan CF81 8TP
ABSTRACT
Hieracium cacuminum, Summit Hawkweed, is a rare
endemic Welsh hawkweed which has been confused
with H. siluriense. A review of the records and field
work showed that 240 plants are known in three
sites; it was not refound in three other sites. It occurs
on Old Red Sandstone cliffs and rocks in the Brecon
Beacons. It is ‘Endangered’ under the IUCN Threat
Criteria.
KEYWORDS: Brecon Beacons, Endemic, Hieracium
siluriense, IUCN Threat Criteria, Lectotype, Wales
INTRODUCTION
Hieracium cacuminum (Ley) Ley, Summit
Hawkweed or in Welsh Heboglys y Copa, and
H. siluriense (F. J. Hanb.) P. D. Sell, Silurian
Hawkweed or in Welsh Heboglys y Silwriaid,
are two Welsh endemic hawkweeds which have
been confused historically as a result of mixed
material being cited with the original des-
cription of H. cacuminum by Ley (1895).
Consequently, the distribution information in
Ley (1895, 1909), Pugsley (1948) and Sell &
West (1968) included both species. Sell &
Murrell (2006) have recently clarified that the
material on which H. cacuminum was based
referred only to material collected in 1888 on
the central Brecon Beacon cliff, and the other
records cited belonged to H. siluriense. In order
to clarify the distribution of H. cacuminum, a
Red Data Book species (Wigginton 1999), and
to provide an IUCN Threat Category as
required under the Global Plant Conservation
Strategy (Secretariat for the Conservation of
Biodiversity 2002), the records and ecology of
H. cacuminum were reviewed, along with fresh
field surveys, and are reported in summary
herein; full details are held by T. Rich and are
available on request.
Hieracium cacuminum was first described as
H. diaphanum var. cacuminum by Ley (1895).
A lectotype has been selected by P. D. Sell
from material collected from a stream side,
Brecon Beacons, 8 August 1888, A. Ley (herb.
Ley, CGE) and is hereby designated by P.D.S.
Hanbury (1904) used Ley’s epithet when he
transferred the variety to H. vulgatum. Later
Ley (in Linton 1905) transferred it to H.
demissum, and then raised it to species status
after the Scandinavian Hieracium expert G. A.
H. Dahlstedt had seen material in 1907 (Ley
1909).
Summary of synonymy:
Hieracium cacuminum (Ley) Ley, J. Bot. 47:
51 (1909).
=H. angustatum (Lindeb.) Lindeb. subsp.
cacuminum Zahn, in Engl., Pflanzenr. 76
(IV, 280): 471 (1921).
=H. demissum Strömf. var. cacuminum Ley in
W. R. Linton Brit. Hier. 74 (1905).
=H. diaphanum Fries var. cacuminum Ley, J.
Bot. 33: 86 (1895).
=H. vulgatum Fries var. cacuminum Hanb. in
Bab. Man. ed. 9, 258 (1904).
Pugsley (1948) regarded H. cacuminum as an
anomalous member of section Tridentata. Sell
& West (1968) and Sell & Murrell (2006) treat
it as a member of section Oreadea. The English
and Welsh names are derived from the Latin
cacumen = peak, extreme top.
*e-mail: tim.rich@museumwales.ac.uk

T. C. G. RICH & P. A. SMITH
464
V.C. 42 BRECON
‘Brecon Beacons’ (SO02)
Brecon Beacons, central cliff 14 July 1886 A. Ley CGE
Brecon Beacons, stream side 8 August 1888 A. Ley CGE (Lectotype), BM, NMW
Brecon Beacons 25 August 1890 A. Ley BM, Pugsley (1948)
Brecon Beacon, on the face of the cliff
near the summit
26 August 1890 A. Ley BM
Brecknock Beacon (=Brecon Beacon),
precipice of the
26 August 1890 A. Ley & W. H.
Purchas
CGE
Brecon Beacons, sandstone mountain
cliff
15 August 1894 A. Ley & W. A.
Shoolbred
BM, CGE, LIV, NMW
Brecon Beacons 28 July 1899 A. Ley BM, CGE, E, LIV, NMW; Set
of British Hieracia no. 116
Brecon Beacons, rocks near the path
between the two beacons (original
locality)
23 July 1902 W. R. Linton BM, CGE, E, LIV, NMW; Set
of British Hieracia no. 116;
Linton (1903)
Cwm Tarrell (SN92)
Cwm Tarrell, by a stream 24 July 1883 A. Ley BM
Cwm Tarrell August 1888 A. Ley BM
Cwm Tarrell 1890 A. Ley BM, Hanbury (1894)
Head of Cwm Tarrell, rocky
mountainside
9 July 1895 A. Ley CGE, Ley (1909)
Glyn Tarrell, cultivated June 1953 P. D. Sell CGE
Glen Tarrell, rocky outcrop at head of 10 July 1959 C. West CGE
Taf Fechan (SO01)
Taf-fechan, sandstone cliffs 15 August 1894 W. A. Shoolbred NMW
Taf Fechan, 1 mile above the Ystrad 23 July 1900 A. Ley CGE
Fan Gyhirych (SN8818)
Y-fan-Gihirich 4 August 1898 A. Ley CGE, Ley (1909)
Glyn Collwng (SO0519)
Rocks at the head of Glyn Collwng
(limestone)/ Collwng Daren, east
side above railway
18 July 1908 A. Ley CGE, Ley (1909)
V.C. 44 CARMARTHEN
Llyn y Fan Fach (SN8021)
Llyn y Fan Fechan, crags of 3 August 1899 A. Ley CGE, Ley (1909)
Cultivated
ex Brecon Beacons June 1898,
28 July 1899
A. Ley BM, CGE, BEL, LIV
TABLE 1. REVISED HISTORICAL RECORDS OF HIERACIUM CACUMINUM
IDENTIFICATION
Hieracium cacuminum is illustrated in Figure
1. Key field key identification features separ-
ating it from most other Hieracium species in
South Wales are the flexuous stem with 3–6
stem leaves decreasing in size up the stem and
without a clear basal rosette at flowering, and
the few-headed inflorescence of capitula with
dark involucres and very broad (1·7–2·3 mm
wide), obtuse outer involucral bracts. Vegetative
plants have similar rosette leaves to the lower
leaves on the stems of flowering plants, but
where similar species (such as H. siluriense)
were present and there was doubt about the
identification, these were not recorded.

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HIERACIUM CACUMINUM
FIGURE 1. Hieracium cacuminum and H. siluriense. A–K, Hieracium cacuminum. A, Whole shoot. B–G, Stem
leaves from base showing decrease in size up stem (details of hairs not shown). H, First year rosette. I, Bud. J,
Capitulum. K, Involucral bract. S, Involucral bract of H. siluriense. Scale bars 1 cm. Del. T. Rich.

T. C. G. RICH & P. A. SMITH
466
Hieracium siluriense differs from H.
cacuminum in usually having at least a loose
basal rosette with 0–2(–3) stem leaves and
narrower (to 1·7 mm wide), acute or subacute
outer involucral bracts. The number of stellate
hairs on the margins of the involucral bracts
varies in both species, but in general there are
more in H. siluriense. Full descriptions of both
species are given by Sell & Murrell (2006).
DISTRIBUTION
Historical records were compiled from herbaria
(BEL, BM, CGE, E, LIV, NMW), literature
and the Hieracium database maintained by D.
J. McCosh. The revised records of H.
cacuminum are given in Table 1. Hieracium
cacuminum has been recorded in six sites in
two vice-counties in the Brecon Beacons in
Wales, where it is endemic.
The historical records were used to direct
field work, principally carried out in July 2004.
Voucher specimens have been placed in the
Welsh National Herbarium (NMW).
BRECON BEACONS (CENTRAL CLIFFS)
105 flowering H. cacuminum plants were
found scattered along the cliff ledges on the
NE facing side of Pen-y-fan on Old Red
Sandstone between SO013215 and SO017212.
They were often in clustered subpopulations,
characteristically occurring on the sides of
steep ‘alcoves’ formed by streams eroding the
cliffs. The population estimate is a minimum as
the crumbling sandstone cliffs are difficult to
access safely. Hieracium siluriense is also
present on the cliffs in greater numbers.
Other crags of the central Brecon Beacons
were also searched. Cribyn (SO0221) had
some suitable ledges, with some H. siluriense
and an unknown species. Craig Cwm Cynwyn
(SO0220) had locally frequent H. siluriense
and one clump of H. argenteum Fr. The rocks
on the NE side of Fan y Big (SO0320) and
Craig Cwarell (SO0420) were rather acidic and
no Hieracium was seen. Corn Du (SO0021)
had no suitable ledges.
CWM TARRELL, CRAIG Y FRO
Cliffs, rocks and gullies at the head of Cwm
Tarrell were searched and H. cacuminum was
found in two places on Craig y Fro. Nineteen
flowering and c. 100 vegetative plants occurred
on Old Red Sandstone cliffs by a waterfall at
SN973203, and 4 flowering and 10 vegetative
plants occurred on a small west-facing cliff at
SN970206. At least five other Hieracium species
were also present including H. siluriense.
FAN GYHIRYCH
The north-facing corrie has a low line of cliffs
with a strongly calcifuge flora, and the only
hawkweed seen was one patch of H. sparsi-
folium Lindeb.
GLYN COLLWNG
Two flowering plants of H. cacuminum were
found on the rocks on the west side of the
waterfall of Nant Bwrefwr, immediately out-
side the car park at SO055175, with H. cf.
diaphanum agg. Two other Hieracium species
were collected further upstream. No H.
cacuminum was found elsewhere.
TAF FECHAN
The imprecise nature of the records made
searching difficult, and no H. cacuminum was
found in areas searched. Hieracium siluriense
occurred at and below Neuadd Reservoir, and
other species were found downstream in
shaded woodlands. No H. cacuminum was seen
on Graig Fan Ddu (SO0119) or Craig Gwaun
Taf (SO0020).
LLYN Y FAN FACH
No H. cacuminum was found during extensive
searches of the cliffs above the lake in 1999
and 2002, and it is probable that intensive
sheep grazing has eliminated this and up to
seven other hawkweeds which were recorded/
collected by A. Ley 100 years ago.
The records are mapped in Figure 2. A total of
c. 240 plants were seen in three sites in three
hectads in one vice-county. It was not refound
in three sites, but some of the localities are
very imprecise and the original site may not
have been found.
BIOLOGY AND ECOLOGY
Hieracium cacuminum is a polycarpic peren-
nial which is dispersed by seed. Buds of two
capitula were excised with scissors to remove
the stigmas and anthers in a green-house, and
covered; seeds were set in both excised and
control buds, showing that reproduction is
apomictic (voucher in NMW). The chromo-
some number is not known, but it is likely to
be polyploid.

467
HIERACIUM CACUMINUM
All populations of H. cacuminum occurred
on low cliffs of Old Red Sandstone, either
rooted in crevices or on immature soils derived
from the sandstone. The ledges have vegetation
10–30 cm tall, with a moderate mixture of
species. Typical species associated with H.
cacuminum were Festuca ovina L. agg.
(including F. vivipara (L.) Sm.), Solidago
virgaurea L., Luzula sylvatica (Huds.) Gaudin,
Deschampsia flexuosa (L.) Trin, Rhytidia-
delphus loreus (Hedw.) Warnst. and
Polytrichastrum alpinum (Hedw.) G.L. Sm. In
a few places H. cacuminum is also associated
with more calcicolous species such as
Campanula rotundifolia L. and Thymus
polytrichus A. Kern. ex Borbás. The upland
cliffs of Pen-y-fan in which H. cacuminum
occurs are probably best ascribed to the U16
Luzula sylvatica – Vaccinium myrtillus cliff
ledge vegetation of the national vegetation
classification (Rodwell 1992).
All the sites are heavily grazed by sheep, and
H. cacuminum is confined to ungrazed ledges
and rocks. It is likely to be susceptible to
grazing, like most other Hieracium species.
Soil pH, measured with a pHep2 Hanna
pocket-sized pH meter in a 50:50 mixture with
distilled water of soil samples collected from
around the roots, were pH 3·9 (ledge) and 7·1
(by waterfall) at Craig y Fro, and pH 3·7, 4·2
and 4·5 from ledges on Pen-y-fan. This range
suggests that it is tolerant of both acid and
calcareous soils. The soils were all damp but
not waterlogged.
The altitudinal range was c. 480 m at Craig y
Fro to c. 650 m on Pen-y-fan.
CONSERVATION
Under the IUCN (2001) Threat Criteria, H.
cacuminum qualifies as ‘Endangered’ (total
population less than 250 individuals, popu-
lation declining). The remaining populations on
Pen-y-fan and Craig y Fro are probably toler-
ably safe, as they are within the Brecon
Beacons SSSI and SAC within the Brecon
Beacons National Park. Although these
designations offer no specific protection for H.
cacuminum, the SAC is designated for the
acidic and calcareous chasmophytic vegetation
and the cliff ledge vegetation, in which H.
cacuminum occurs. The two plants at Nant
Bwrefwr are not in any designated sites, are
close to a public car park and picnic area, and
are highly threatened.
The biggest threats to H. cacuminum are
from rock-falls, which could eliminate local
populations, and over-grazing. It is possible
that the decline in the three sites is attributable
to over-grazing, though without knowledge of
the precise original localities this is difficult to
assess. Forestry or development of reservoirs
could also be responsible for the loss from Taf
Fechan. A reduction in grazing throughout the
Brecon Beacons would benefit this and other
Hieracium species.
Seed was collected from Craig y Fro and
Pen-y-fan for the Millennium Seed Bank on 23
July 2004. No live collections are currently
held in cultivation in botanic gardens.
ACKNOWLEDGMENTS
We would like to thank Joe Daggett and the
National Trust, Andy Jones, David McCosh,
Graham Motley, Mike Porter, Robin Walls and
the Keepers of the Herbaria for access to
libraries and specimens, and Peter Sell for
allowing us to publish his lectotypification.
The Countryside Council for Wales funded
collation of the historical records.
FIGURE 2. Distribution of Hieracium cacuminum.
(z 2004–2005. | pre-2004. ± = errors, mostly
referable now to H. siluriense).

T. C. G. RICH & P. A. SMITH
468
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