UBC Publications

UBC Publications

UBC Publications

Davidsonia Sep 1, 1973

Item Metadata


JSON: davidsonia-1.0115072.json
JSON-LD: davidsonia-1.0115072-ld.json
RDF/XML (Pretty): davidsonia-1.0115072-rdf.xml
RDF/JSON: davidsonia-1.0115072-rdf.json
Turtle: davidsonia-1.0115072-turtle.txt
N-Triples: davidsonia-1.0115072-rdf-ntriples.txt
Original Record: davidsonia-1.0115072-source.json
Full Text

Full Text

Fall 1973 Cover
Late flowering, early fruiting branch of
Sitka Mountain-ash, Sorbus sitchensis
Typical tufted growth of
Dicranoweisia cirrhata, a
common rooftop moss.
Fall 1973
Davidsonia is published quarterly by The Botanical Garden of The University of British
Columbia, Vancouver, British Columbia, Canada V6T 1W5. Annual subscription, four
dollars. Single numbers, one dollar. All editorial matters or information concerning subscriptions should be addressed to the Director of The Botanical Garden.
A cknowledgements
The pen and ink sketches on the covers as well as the plate on page 31 are by Mrs. Lesley
Bohm. All other sketches and vignettes are by Patricia Drukker-Brammall through the
courtesy of Dr. W. B. Schofield. Photographic credits are as follows: p. 28, top Dr. C. J.
Marchant, bottom Dr. R. L. Taylor; p. 29 Dr. R. L. Taylor. 'Mosses on Rooftops' was
prepared by Dr. W. B. Schofield of the Botany Department, UBC. Mrs. Sylvia Taylor
researched the article on Sitka Mountain-ash. Mosses on Rooftops
Mosses are opportunists. Whenever a suitable site becomes available, they invade it and
persist until crowded out or forcibly removed. Since readily available moisture and
nutrients are the main requirements of mosses, the humid coast of British Columbia provides ideal conditions for their growth and development.
It is not surprising, then, that mosses occupy rooftops. The presence of shade trees
nearby to keep the roof persistently moist even when rain is not falling, coupled with a rain
of ash from a fireplace chimney, provides superlative conditions for moss growth. The
only requisites that remain are a suitable substrate for establishment, and the arrival of
the moss. Most types of shingle will permit mosses to become established, especially as the
shingles become older. Thus composition shingles, asbestos shingles and wooden shingles
all provide a favourable site. A metallic roof inhibits moss colonization and heavily tar-
impregnated roofing will not permit mosses to colonize so long as the surface is smooth.
In the latter case, however, in any joints and crevices where wind-borne fragments (plus
moisture and nutrient minerals) can accumulate, a moss can establish itself and expand its
colonies outward from such initial populations.
Mosses usually first occupy sites on the shingles directly above the eaves on detritus that 2 /
has accumulated in the eaves trough, valleys or other depressions on the roof. Mosses tend
to thrive well in the winter, when moisture is abundant and illumination and temperatures
are low. During the summer these same mosses may remain dormant much of the time,
either through desiccation or as a result of the natural cycle of growth in these plants.
In winter or spring most of these mosses produce fruiting bodies. Dicranoweisia cirr-
hata, an extremely common moss of roofs, produces its fruiting bodies in winter and they
mature and shed their millions of spores to the wind. This same moss also produces minute
vegetative reproductive bodies, called gemmae. These, too, occur in great abundance and
can be wind-blown to new sites. This moss is also common on roadside tree-trunks. It is
this moss that often outlines the margins of composition shingles with narrow velvety turfs.
In the winter, too, the moss Ceratodon purpureus produces reddish spears that will
become mature fruiting bodies in the spring. Dense colonies of these spears give a reddish
pink flush to the vivid greenery of the turfs of moss. Some species of Bryum often grow
associated with the Ceratodon and add to the colour.
Variant colours of green and a change in texture are produced by the various species
of Rhacomitrium that can become established on rooftops. Rhacomitrium lanuginosum,
when dry, forms grayish rounded cushions, whereas R. canescens is whitish yellow in the
same state. Rhacomitrium heterostichum usually forms darker, smaller tufts. When moist,
these mosses produce patches of grayish green (R. lanuginosum, R. heterostichum) or
bright yellow-green (R. canescens).
Habit of individual plant of Dicranoweisia
cirrhata magnified approximately 8X. Typical growth of mosses on weathered asphalt composition shingled roof. Species illustrated
include Dicranoweisia cirrhata and Rhacomitrium canescens.
purpureus AX
Mosses and lichens adorn
wooden roof of Gate to Nitobe
Memorial Garden. In the
photograph the lichens are
the irregular whitish areas and
are very different in structure
and appearance from the
velvety cushions of mosses.
I cm An unusually large assemblage of mosses
on the roof of the Waiting Arbour near
the Teahouse in the Nitobe Memorial
Garden. Many of the mosses occur rarely
on rooftops. The dominant moss is
Hylocomium splendens. Others are:
Dicranum howellii, Pohlia nutans,
Polytrichum juniperinum, Rhytidiadelphus
loreus, Plagiothecium undulatum,
Dicranoweisia cirrhata and Aulacomnium
Finally, Tortuta ruralis and T. princeps can form almost pure dense colonies on shaded rooftops, particularly garages where trees overhang, providing shade with associated persistence of moisture, and also
an abundance of nutrients from rainwash through the leafy canopy.
These mosses enhance the beauty of a roof by contributing a richness of variable colours and textures.
In other countries, as in Japan, they also flourish on thatched roofs. Naturally, opportunists from the indigenous flora are involved, but the resultant rich textures and interplay of colours are similar.
So far as I know, there has never been an attempt to exploit this natural enhancement of the beauty of a
roof. The main problem would be to guarantee that the presence of the moss would not aid in the deterioration of the roof. Under normal conditions the expansion of the moss colony can result in pushing up the
edges of the shingles, particularly if they are composition shingles. In wooden shingles, however, if a roof
begins to leak, it is unlikely to be caused by the moss, but results from natural deterioration of the roof
whether or not the moss is present.
Editors' note: Additional information concerning common mosses occurring in British Columbia can be found in
a recent publication by Dr. Schofield entitled: 'Some Common Mosses of British Columbia'. This useful guide was
published in 1969 as Handbook No. 28 by The British Columbia Provincial Museum with illustrations by Patricia
Drukker-Brammall. 30
SorbuS sitchenstS Roemer
Member of the Family Rosaceae
Natural Distribution
Sorbus sitchensis occurs from the coastal region of Alaska south of 54°N, south through the Cascade and
Olympic Mountains of Washington and the Cascades of Oregon to northern California, and east to eastern
British Columbia, Waterton Lakes National Park in Alberta, northern Idaho and northwestern Montana.
It has been reported from the Yukon Territory. It is widely distributed throughout British Columbia, very
common on the high mountains between Grand Forks and Rossland and extending northward beyond
McLeod Lake.
Sorbus sitchensis is usually found at moderate-to-high altitudes in the mountains. In British Columbia it
is most abundant above 3000' near the coast, but above 4000' in the Interior, in open areas such as the
edge of a meadow or rockslide. Maximum development occurs about headwaters of small mountain streams,
springy depressions, in moist, sandy and mucky soils.
An erect, several-stemmed, nearly glabrous, deciduous shrub 1.2-2.5 m tall, or a small tree 4.5-6.0 m
tall and 15 cm in diameter. If a tree, then with a handsome, roundtopped head. In rocky alpine situations
at higher latitudes, 5. sitchensis is usually a low shrub only 30-61 cm high. In poor situations, shrubs may
have a few thin stems to 2.5 m tall with a few leaves and berries near the top.
The root system is taprooted with many fine feeder roots. Occasional suckering may occur.
The bark is reddish-purple, tardily glabrous, becoming grayish-red with age, occasionally becoming
scaly and thin.
The twigs are stout and rusty pubescent when young, becoming brown and glabrous with age. The wood
has the smell and bitter taste of cherry when broken. Conspicuous and elongated horizontal lenticels are
present. The pith is five-angled, continuous and brownish.
The wood is moderately light, low in strength, close-grained. The heartwood is pale brown, the sapwood
nearly white. The wood is of no commercial value.
Buds are subconical or oblong. Terminal buds up to 12 mm long, laterals often much reduced. Buds are
solitary and sessile, dull reddish-brown, densely rusty to white hairy to nearly glabrous, with several imbricate bud scales, inner scales more or less pubescent with long hairs often matted in gum, leaf blade rudiments
often occurring at tip. Many lateral buds remain undeveloped.
Leaf scars are alternate, scarcely raised, narrow, crescent shaped, half encircling the twig, bundle traces
3 or 5 or exceptionally 7, stipule scars lacking.
Leaves are alternate, pinnately compound, 10-20 cm long, stipules persistent or tardily deciduous. Leaflets 7-11 (-15), elliptic ovate or narrowly ovate to elliptic or obovate, rather thick, glabrous and dark
green above, paler beneath and often persistent pubescent with rufous hairs along the mid-vein, (1.5-)
2-5 (-7) cm long, 1/3-2/5 as broad, rounded to semi-truncate at apex, but may be acute. The leaflet margins
are coarsely and sharply serrate from near the base to the apex or almost entire. The terminal leaflet is
petiolate, lateral leaflets are mostly sessile.
Plants flower from May-June in British Columbia, May-August in other parts of the range. The inflorescence is a large terminal compound corymb, pubescent, 15-80 flowered, 5-10 cm across. The pedicels are
rusty hairy or sparsely white hairy to nearly glabrous. Flowers about 6 mm across, sweet scented, although 31
FIGURE 1. Sorbus sitchensis Roemer. A. fruiting branch, B. inflorescence, C. habit, D. flowtr bud, E. single flower, F. jingle fruit. the scent may be obnoxious to some people. Calyx turbinate-obconic, glabrous to sparsely pubescent, adnate
almost to top of the ovary with a short free hypanthium, 5 lobes triangular, persistent. Petals 5, white to
cream, (3-) 4-5 mm long, rhombic to elliptic, usually very short-clawed, sparsely pilose on the upper surface
near the base, deciduous. Stamens 15-20, filaments broadened slightly near the base, usually shorter than
the petals. Styles 2-5, distinct, (1.5-) 2-3 mm long, villous at base. Ovary compound, 1/2-4/5 inferior, 2-5
carpels (usually 3), hairy at least at the top. Ovules 2 in each locule.
Fruit a fleshy berry-like pome, 6-8 (-10) mm long, ellipsoid to subglobose, orange to coral red to purple
red, glaucous, with a slight bluish cast, 2-5 celled, carpel wall thin-papery. Fruit is acid and matures July-
September depending on location. The fruit may remain attached all winter if not eaten by birds. Seeds 1-2
to each locule, 3 mm long, brown, elliptic and somewhat flattened.
Seed can be sown in the fall as soon as it is ripe or can be stratified for 3 months at 40°F and then sown.
If germination has not occurred after 3-4 months, a further 3 months' cold treatment will usually result
in success. Layering is also used. Varieties and rare forms are usually budded or grafted onto a related
species, or onto Sorbus aucuparia (European Mountain-ash).
Easily transplanted and fairly quick to establish.
Conditions for Cultivation
The shrub is relatively fast growing. The recommended hardiness zone in Canada is zone 3. Sorbus
sitchensis needs ordinary well-drained loamy soil with a pH of about 6.0. It prefers full sun rather than
partial shade. No regular pruning is necessary.
Landscape Value
The genus Sorbus is widely planted as ornamental shade trees in sunny borders or as isolated lawn specimens because of their attractive white flowers, striking foliage which usually turns orange-red in the fall,
and especially the ornamental fruits which often remain on the branches all winter. They are ideal for
O^ adding a colourful accent in the fall to almost any planting. Sorbus sitchensis itself is rather rare in cultiva
tion although it is an extremely attractive native shrub or small tree which is well suited to planting on
rocky slopes. It has occasionally been planted as a boulevard tree in Victoria (Szczawinski and Harrison
1973). The European Mountain-ash, S. aucuparia, is most commonly found in gardens and is even locally
naturalised from Labrador to British Columbia. Birds are attracted by the berries.
Apparently not available from any nurseries in British Columbia.
Varieties and Ornamental Cultivars
Hybrids between Sorbus sitchensis and S. scopulina Greene (Greene's Mountain-ash) have been reported
but otherwise there seem to be no natural or artificial hybrids.
There are two geographic races which have been recognised. The races differ mainly in the serration of
the leaflets and there are considerable intermediate forms. Sorbus sitchensis ssp. sitchensis (or var. sitchensis) has the leaflets toothed (about 16-40 teeth) from the apex to usually 1/2-3/4 (-4/5) of their
length, elliptic to occasionally oblong, acute to rounded at the apex and is found from Alaska and southern Yukon south to northwestern Montana and northern Idaho and to southwestern Alberta. It is not
uncommon in the Cascades of Washington where it is often intermediate to S. scopulina. It is also sometimes transitional to the latter especially in the area between Mt. Rainier and Mt. Adams. Sorbus sitchensis
ssp. grayi (Wenzig) Calder & Taylor (or var. grayi (Wenzig) C. L. Hitchc.) has the leaflets toothed (about
4-16 teeth) primarily only above the middle or is almost entire, oblong to elliptic-ovate, rounded or truncate at the apex and is found in the Cascades from southern British Columbia south through Washington
(where also in the Olympics) to the Sisters in Oregon and perhaps intermittent to northern California. It is
also found in the Queen Charlotte Islands where it is considered the subalpine phase which is found only
at tree line at Takakia Lake and on north-facing open forested slopes at about 1800' on Mosquito Mountain, whereas ssp. sitchensis is a lowland tree of open forests along the shores of saltwater inlets, lakes and
rivers. Other Uses
The wood is of no commercial value but the berries are suitable for making jelly although they have a
sour, mealy taste when raw. The Thompson Indians of British Columbia occasionally ate the berries. The
Bella Coola Indians collected the bark of the root and sometimes the inner bark of the stem at any time of
year, boiled it for an hour, and the hot decoction, preferably strong, but also weak, was drunk for ailments
of the stomach or rheumatism, but not taken for diarrhoea or vomiting. It was said to effect a cure in 1 to
7 days. For rheumatism the hot decoction was sometimes poured into a large box and used as a bath. It
was also used as an eyewash. The berries were rubbed into the hair to remove lice. The Southern Carrier
Indians chewed the bark as a treatment for colds whereas the Gitksan tribe ate the raw crushed fresh fruit
as a strong purgative. The fruits of European species of Mountain-ash have been used to make jellies and
preserves for centuries.
Diseases and Pests
It has proven difficult to find information on diseases and problems specific to Sorbus sitchensis, except
for the two organisms discussed below. The genus as a whole is susceptible to most of the same diseases
and insects common to other members of the Rosaceae, such as Crabapples, and Roses, and particularly to
borer attacks at the base of the tree. These diseases and pests include: Erwinia amplovora 'Fire Blight'; E.
tumefaciens 'Crown gall'; Cytospora spp. 'Canker'; Chrysobothris femorata 'Flatheaded borer'; C. mail
'Pacific flatheaded borer'; Eriophyes pyri 'Pear leaf blister mite' and Pristiphora eniculata 'Mountain ash
sawfly'. The majority of diseases can be prevented or at least minimized by keeping the tree in a healthy
(a) Fungus Diseases
Gymnosporangium cornutum, G. tremelloides and G. nootkatense 'leaf rusts' have all been reported on
wild Sorbus sitchensis (Toms 1964, Parmelee 1971). Circular light yellow thickened spots appear during
the summer, orange cups develop later on the lower surface of these spots.
The rust may be controlled by using sprays recommended for rust control of Flowering Crabapples
(Malus). If the Mountain-ash is highly prized, and it is practicable, it may be best to remove the alternate
host (Juniperus and Chamaecyparis spp).
(b) Insect Pests OO
Anuraphis rpseus 'Rosy apple aphid' and Eriosoma lanigerum 'Woolly apple aphid' frequently infest
Mountain-ash. The former cause the leaves to curl around them thus protecting the aphids from natural
enemies, sprays and dusts; whereas, the latter feed on wounds on the trunks and branches or migrate down
to the roots where they cause the formation of knots resulting in the production of many fibrous roots and
Both pests are susceptible to natural enemies such as Aphelinus mali, a wasp-like parasite; ladybeetles;
syrphid fly larvae and aphid lions. However, if the season is cold and wet the aphids will develop faster
than the predators—in this case, spray with a dormant oil spray to kill the overwintering eggs.
The generic name Sorbus is from the ancient Latin 'sorbum' for the fruit of the Service Tree (Sorbus
domestica). The specific name sitchensis means "of Sitka"—the tree was first collected in Sitka, Alaska.
Calder, James A. and Roy L. Taylor. 1968. Flora of the Queen Charlotte Islands. Part 1. Research Branch, Canada
Department of Agriculture, Monograph No. 4, Part 1.
Hitchcock, C. L. et al. 1961. Vascular Plants of the Pacific Northwest. Part 3. Saxifragaceae to Ericaceae. University of Washington Press, Seattle.
Lyons, C. P. 1965. Trees, Shrubs and Flowers to Know in British Columbia. (Rev. ed.). J. M. Dent & Sons (Canada)
Ltd. Toronto and Vancouver.
Parmelee, J. A. 1971. The Genus Gymnosporangium in Western Canada. Canadian Journal of Botany 49:903-926.
Smith, H. I. 1929. Materia Medica of the Bella Coola and Neighbouring Tribes of British Columbia. National
Museum of Canada. Annual Report for 1927. Bulletin No. 56:47-68.
Szczawinski, Adam F. and Antony S. Harrison. 1973. Flora of the Saanich Peninsula. Occasional Papers of the
British Columbia Provincial Museum. No. 16. Victoria, B.C.
Toms, H. N. W. 1964. Plant Diseases of Southern British Columbia. A Host Index. Pp. 143-225. Reprinted from
Canadian Plant Diseases Survey. Volume 44. Canada Department of Agriculture Publication, Ottawa.
Viereck, Leslie A. and Elbert S. Little, Jr. 1972. Alaska Trees and Shrubs. USDA Forest Service, Agriculture
Handbook No. 410. Botanical Garden News and Notes
Garden Component Developments—During the past summer attention has been directed to the development of the B.C. Native Garden component. A field collection program in B.C. was initiated to gather
native woody tree and shrub material for incorporation in the B.C. Native area. Construction of the Rock
and Alpine Scree Garden commenced in mid-August and drainage, rock work, pathways and soil filling
were substantially complete before fall rains commenced.
Local Initiatives Program 1973—During the period January to July, 17 persons were hired under the
government-sponsored L.I.P. They formed the core of the labour force in the clean-up and preparation
of the B.C. Native area. Some effort was also directed towards the care and maintenance of the woody
material purchased from Lohbrunner Nurseries.
Visitors—On June 16th and October 13th the Alpine Garden Club of B.C. visited the Botanical Garden to
inspect the expanding collections of alpine plants in the nursery and to see the B.C. Native area and the
Rock and Alpine Scree Garden during the later stages of their development and construction.
Staff Activities—Mr. James O'Friel attended the Western Regional meetings of the International Plant
Propagators Society held this year in Honolulu, Hawaii. Dr. John Neill was elected a Fellow of the Canadian Society of Landscape Architects in May 1973. Dr. Roy L. Taylor, Dr. Bruce MacBryde and Dr. Christopher J. Marchant attended the first meeting of the International Conference for Systematics and Evolutionary Biology in Boulder, Colorado in August. Congratulations to Mrs. Nancy J. Turner on completion
of her doctorate research in Ethnobotany and the attainment of her Ph.D. degree. She now holds a contract
appointment at the Provincial Museum in Victoria. Dr. Chris Marchant continues to serve on the executive
committees of the Canadian Botanical Association and the Alpine Garden Club of B.C. Mr. Kenneth
Wilson and Mr. Leonard Gibbs are members of the executive committee of the Vancouver Rose Society.
National Botanical Garden System for Canada—1973 saw the development of a major proposal to the
Federal Government concerning a plan for the establishment of a National Botanical Garden System. The
proposal, funded by the Minister of State for Science and Technology, was prepared by Dr. Roy L. Taylor
(Chairman), Dr. Leslie Laking and Dr. Leo A. Dionne and approved by the six-man Organizing Committee for A National Botanical Garden System for Canada. This latter body was established in October 1971
to further the development of a botanical system for Canada. The feasibility study was submitted to
MOSSTin April and has been subsequently sent to all participants of the October 1971 Symposium held at
the Royal Botanical Gardens at Hamilton. Persons interested in adding support or obtaining information
concerning this proposal can contact any member of the committee or write directly to the Minister of
State for Science and Technology.
Data                                                          1973
Mean temperature
Highest temperature
Lowest temperature
Grass minimum temperature
Total rainfall/No. days with rainfall
Total snowfall/No. days with snowfall
Total hours bright sunshine/possible
Max. wind speed (m.p.h.) for 1 hour/
12/NW & E
Mean mileage of wind at 3'
Mean mileage of wind at 40'
*Site: The University of British Columbia, Vancouver, B.C. Canada
Position: lat. 49°15'29"N; long. 123°14'58"W. Elevation: 342.6' Rhacomitrium canescens, a widely distributed
species throughout the circumpolar regions of the
Northern Hemisphere and a frequent visitor
on roofs in the Vancouver area.
Rhacomitrium lanuginosum, a widespread moss
species that occurs at all elevations except in
arid regions of the Northern Hemisphere. The species
is also found in the Southern Hemisphere.
A striking gray-green moss occasionally found on
rooftops in coastal British Columbia. Fall leaves of Quercus coccinea, the Scarlet Oak.
A striking tree often used as an attractive
ornamental in the lower mainland of British Columbia.
Volume 4      Number 3
Fall 1973
Mosses on Rooftops    27
Sorbus sitchensis, Sitka Mountain-ash    30
Botanical Garden News and Notes    34
Climatological Summary    34
"price printing ltd.


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items