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Mossy trunk

The Crytogamic Carpet --Mosses in Seattle

Moss Ecology

    Though humble in size, mosses play significant roles in nature. Chiefly, they are plants which thrive in those habitats where more complex, larger plants are unable to grow, such as on our roofs and in the cracks of our streets. Clearly, mosses are tough and adaptable. Notice how they can shrivel up during dry spells in order to conserve their vital water, and then become lush again after being refreshed by rainfall. Notice how well they spread and multiply. Their countless tiny reproductive cells are borne by the wind like pollen to every imaginable place. We see mosses covering the forest floor, growing on exposed, disturbed soils, spreading over tree trunks, logs, walls and rocks.
    But ironically, certain mosses find themselves in the position of those people who, after politely holding open a door to admit others, find it closed to themselves. As an example of plant succession, imagine the following: a gigantic pile of heavy clay soil is excavated from a construction site, trucked to a meadow, and dumped in a big pile. By the following spring it is covered with a thick, colorful carpet of cord moss (Funaria hygrometrica), a pioneer species. But, inevitably, grasses and other plants will invade the pile and eventually drive out the moss. In time trees will grow up and shade out the other plants. At this point other sorts of mosses will return, to grow on the trees and on the shaded ground.
    Within and underneath these green, living carpets, many plants, micro-organisms and small insects live. The licorice fern often grows with moss. Bushtits and other birds are kept happy building nests with mosses. Indeed, the only enemies of mosses are certain folks who cannot tolerate mosses on their roofs, or in their lawns and gardens. In this case, the meek do inherit the earth.

Seattle's Mosses

    Seattle has an interesting, very rich moss population. How many different species grow within the 100 square miles of the city? We are unsure, but around 100 is a good estimate. (The city of Vancouver, B.C., with a climate similar to Seattle's, has more than 130 species of moss, so more may eventually be found in Seattle.) As with the trees and shrubs in Seattle, a certain few species are dominant and extremely abundant; a much larger number are rare and often restricted to special micro-habitats. For example the peat moss (Sphagnum squarrosum) appears to grow only in one place in Seattle: the cattail marshes of Union Bay. In general, Seattle has almost all of the very common mosses which occur in lowland western Washington.
    The University of Washington has a still-expanding moss herbarium boasting more than 70,000 specimens. Many species which were collected in Seattle parks from the 1890s to the 1940s seem to be either very rare or extinct now. In fact, Seattle mosses simply have not yet been thoroughly studied (nor has its flowering-plant population been adequately documented). We who investigate the matter continue to discover new and noteworthy finds, including rare mosses. One moss recently collected from the mud at the Montlake Playfield, not far from the Arboretum, proved to be Amblystegium saxatile which had apparently been collected only once before in this state --in the 1890's near Mount Rainier!
    Because of its unusually wide diversity of habitats suitable for mosses, the Arboretum probably has more different kinds of mosses than any other place in the city; perhaps 70 can be found growing there. A significant few have been found growing only at the Arboretum, including Eurhynchium serrulatum, which must have been introduced with some planting-stock, as it had not heretofore been known west of the Mississippi River! Mosses even grow on our freeway now.

Moss Study and Identification

    Dr. Elva Lawton has been at the University of Washington for over 20 years. She is curator of the moss herbarium, has taught many students about mosses, and is the author of The Moss Flora of the Pacific Northwest. (Dr. Lawton passed away since this article was published; she was born in 1896 and died in 1993) Yet there are mosses that she cannot positively identify without microscopic analysis. This is because some mosses are so utterly small and so similar to related species that even the experienced eye cannot always distinguish them without magnification.
    But a number of common mosses are quite as distinct and easy to recognize as are eagles and chickadees. Features used for field identification of mosses include their general appearance, size, color and habitat. With experience, the knowledge of which mosses are common in an area --and which rare-- is also of aid. It is important to remember that at different times of the year mosses exhibit seasonal changes, and take on a different appearance depending upon how moist or dry they are.

Some Common Mosses

    People interested in being able to name some mosses will find the following selection a good set with which to start. We illustrate and describe mosses which are very common to ubiquitous in their particular habitats, and are sufficiently distinctive to be readily recognized.
    On exposed soil with fluctuating moisture, such as is found in rockeries, expect to see the big juniper haircap moss (Polytrichum juniperinum). Notice that it grows in large mats or clumps and bears a remarkable similarity to the juvenile foliage of junipers or the "Moss" cypress (Chamæcyparis pisifera 'Squarrosa'). During dry weather the leaves of the juniper haircap moss tightly hug the stem, like a closed umbrella; in moister conditions they stick out like bristles. The color is dull green mixed with rich brownish red hues. The 'haircaps' (called calyptras), the covering over the erect spore-producing structure, are pale yellow and silky, and very showy when present. The juniper haircap is one of the larger and more conspicuous mosses in Seattle, and has only one look-alike to confuse you: Polytrichum piliferum.
    Another common moss of well-drained, exposed soil is the purple horntooth (Ceratadon purpureus). It is tiny, grows in small clumps and is distinctly purple during much of the year.
    In (acidic, moist Seattle) lawns the most common, abundant and luxuriant moss is the redstem bentleaf moss (Rhytidiadelphus squarrosus). It grows extremely thickly and gives a decidedly greenish-yellow color to lawns. This species and the other three common lawn mosses in Seattle are more readily found in lawns than in the wild. If the moss in your lawn has reddish stems and the leaves are obviously bent downwards at sharp angles, it is Rhytidiadelphus squarrosus. Otherwise it is probably one of the following: Brachythecium albicans, Calliergonella cuspidata, or Pseudoscleropodium purum (an introduction from Europe). Applications of lime and iron-rich fertilizers tend to discourage these lawn mosses.
    On cement walls many species grow, most of which are difficult to identify. The silver cushion moss is an exception. In several common mosses which grow on concrete we see a silver-grayish color present because the tips of the moss leaves are long, colorless awns which reflect the light. The silver cushion moss (Grimmia pulvinata) is a common and obvious example. Wall moss (Tortula muralis) is also extremely common on cement, but is greener and a bit larger. It is safe to say that an old cement wall with mosses will surely have both of these species, as well as several others.
    A dendroid (treelike) moss of our woods, which resembles a miniature palm, is called Menzies' tree-moss (Leucolepis Menziesii). It grows on moist maple trunks or rotten logs, and in the humus-rich soil of our forests. It is not always easy to find, but is unmistakable. It can only be confused with the very, very rare (in the city) big tree-moss (Climacium dendroides). In Seattle, Climacium is found only in the muck of Foster Island, and even there is not as abundant as Menzies' tree-moss.
    In moist shady woods, on rotten stumps and logs, lovers' moss (Aulacomnium androgynum) grows. It is rendered very distinctive by its non-sexual reproductive equipment. Like other mosses, it can send up spore-filled capsules. . . but in addition it produces asexual 'gemmae' in great abundance. These little round balls are borne on tiny pegs above the uppermost leaves of the individual moss shoots. If you look for lovers' moss, you will find it, for although tiny, it is abundant. Many other mosses also grow on decaying wood in the forest. The very, very pale white-green one that forms large flat mats is Plagiothecium undulatum.
    Slender beaked moss (Eurhynchium prælongum Stokesii) is surely to be found in the woods. It is regularly encountered on mossy trunks of maple, in clumps of lady fern, on rotten logs or clay soil, or hanging in strands from shrubs in very moist ravines. It cannot be readily distinguished by the beginner because so many look-alikes occur, but is so common that it will certainly be seen.
    Orthotrichum Lyellii is the most common of five species of Orthotrichum in Seattle. It is also the largest. These mosses are usually found high up in willows, alders, madronas and maple trees. When you find a fallen limb from such a tree, you will probably find this moss if any at all are present --the habitat is too dry for other species. Lichens can tolerate the conditions where we find Orthotrichum, as can one other common moss, Dicranoweisia cirrata.
    Mountain fern-moss (Hylocomium splendens) is a moss to look for. It is very large and conspicuous and resembles miniature fronds of ferns. It is common in forests of the Puget Sound lowlands, except in Seattle. Although it has been found here in the past, it is now either very rare or extinct. If anyone locates Hylocomiumin the woods of Seattle, we would be glad to know about it! (Plenty was located in March 1983 at Camp O.O. Denny Park, a City of Seattle park on the east side of Lake Washington)

The Mosses Speak . . .

    In the old-fashion Language of Flowers, the birch tree signified gracefulness, the cabbage profit, the fern simplicity, the lichen solitude, the mushroom superstition, the nettle cruelty, the rose beauty and the thistle austerity. A tuft of moss stood for maternal love. We appreciate the beauty that these humble plants lend to barren rock, tree trunk and soil, and their comforting carpet of green.


- Lawton, E. 1971. Moss Flora of the Pacific Northwest. The Hattori Botanical Laboratory, Nichinan, Miyzuki, Japan.
- Lawton, E. and L. Elliott. Common Mosses of Western Washington. Unpublished; a classroom handbook with illustrations reprinted by permission from Lawton, 1971.
- Noll, H.R. 1852. The Botanical Class-book and Flora of Pennsylvania. O.N. Worden, Printer, Lewisburg, Pennsylvania.
- Schofield, W.B. 1969. Some common Mosses of British Columbia. British Columbia Provincial Museum, Victoria, British Columbia. (Handbook No. 28)

A List of the Mosses found in Seattle

    Some of the following are common, others rare, and a few have not been collected since the 1930s. Doubtless a few other rare mosses occur in the city, but have not found their way onto this list of 103 taxa, arranged under 24 families (The names used below were current as of 1982 but in the intervening years some have been changed; I would list the new names for you except that I have not kept up with them, and do not have time to learn them).

Sphagnum squarrosum

Tetraphis pellucida

Buxbaumia Piperi

Atrichum Selwynii
Atrichum unudualtum var. gracilisetum
Polytrichum juniperinum
Polytrichum piliferum

Fissidens bryoides

Ceratadon purpureus

Dicranella heteromalla
Dicranella Schreberiana
Dicranella subulata
Dicranoweisia cirrata
Dicranum Howellii
Dicranum fuscescens
Dicranum tauricum

Barbula convoluta
Barbula vinealis var. vinealis
Barbula vinealis var. flaccida
Didymodon tophaceus
Pottia truncata
Timmiella crassinervis
Tortula amplexa
Tortula Bolanderi
Tortula latifolia
Tortula muralis
Tortula princeps

Grimmia apocarpa var. gracilis (stricta)
Grimmia pulvinata
Grimmia trichophylla
Rhacomitrium canescens var. ericoides
Rhacomitrium heterostichum var. heterostichum
Rhacomitrium heterostichum var. occidentale
Rhacomitrium varium

Funaria hygrometrica
Physocomitrium megalocarpum

Epipterygium tozeri
Leptobryum pyriforme
Bryum argenteum
Bryum bicolor
Bryum capillare
Bryum lisæ var. cuspidatum (creberrimum)
Bryum pseudotriquetrum var. bimum
Pohlia annotina
Pohlia longibracteata
Pohlia nutans
Pohlia Wahlenbergii

Leucolepis Menziesii
Plagiomnium insigne
Plagiomnium venustum
Rhizomnium glabrescens

Aulacomnium androgynum
Aulacomnium palustre

Orthotrichum consimile
Orthotrichum Lyellii
Orthotrichum pulchellum
Orthotrichum rivulare
Orthotrichum striatum
Ulota crispa var. alaskana
Zygodon vulgaris

Neckera Douglasii
Neckera Menziesii

Pseudoleskeella tectorum

Climacium dendroides

Claopodium Bolanderi
Claopodium crispifolium
Heterocladium Macounii

Amblystegium juratzkanum
Amblystegium saxatile
Amblystegium serpens
Amblystegium trichopodium var. trichopodium
Calliergion cordifolium
Calliergionella cuspidata
Drepandocladus aduncus
Drepandocladus uncinatus
Hygrohypnum ochraceum
Pleurozium Schreberi

Brachythecium albicans
Brachythecium asperrimum
Brachythecium plumosum
Brachythecium Starkei var. explanatum
Eurynchium oreganum
Eurynchium prælongum var. Stokesii
Eurynchium serrulatum
Homalothecium fulgescens
Homalothecium Nuttallii
Isothecium cristatum
Isothecium stoloniferum
Pseudoscleropodium purum
Scleropodium cespitans var. cespitans
Scleropodium obtusifolium
Scleropodium Touretti var. Touretti
Scleropodium Touretti var. colpophyllum

Isopterygium elegans
Plagiothecium denticulatum
Plagiothecium lætum
Plagiothecium undulatum

Hypnum circinale
Hypnum subimponens

Rhytidiadelphus loreus
Rhytidiadelphus squarrosus
Rhytidiadelphus triquetrus

Hylocomium splendens

(Originally published in the Spring 1982 University of Washington Arboretum Bulletin, pages 12 - 17, along with 1 photograph and line drawings of ten moss species.)


Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert

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