Linda Gregory

As you approach an island from a distance you may see a stand of spruce or lichen-covered granite outcrops. A small bay with a carpet of brown rushes in the shallows may greet you. No matter what time of year you visit an island you will be presented with a colorful landscape due in large part to the flora. June is the blue of irises and the pink of roses. July is a rainbow of colors, the height of bloom. August is goldenrod gold and purple-blue asters. In September warm tan tones emerge with an array of red colored berries. Literally hundreds of interesting wildflowers and other types of plants make their homes on these islands; in this article I will highlight just a few of the common and unique species that you may encounter.


Island Habitats

Maine's coastal islands straddle the boundary between two major biogeographic regions: the northern boreal forest and the eastern deciduous forest. The northern boreal forest contains spruce and fir generally seen midcoast and downeast, while the eastern deciduous forest has oaks and other hardwoods more typical of southern Maine. Islands have plant species that have adapted to saltwater surroundings and are therefore found only along the coast. The size, shape, topography, soil, and substrate of each island, as well as its distance from the mainland, directly affect what plant life grows there. Some islands are mostly rock with little soil, while others have large spruce stands, meadows or marshes. Most have a mixture of several different habitats. On any given island there is a unique combination of factors that affect the island's environment. As a result, the flora of each individual island is also unique.

The majority of island plants are native, or indigenous. However, human use of the islands has influenced what grows there today. Past land uses such as sheep grazing and timber harvesting have had the greatest effect on plant life. About a quarter of the species that you will find were introduced by humans for food, such as apples; or fodder for animals, such as timothy and clover; or by accident, such as bull thistle and Canada thistle, which were probably introduced as weed seed in livestock feed. Species that we often associate with Maine such as lupines (Lupinus polyphyllus) and rugosa rose (Rosa rugosa) are also non-native; both were brought in as landscape plants. The same is true of many common plants seen on islands, such as yarrow (Achillea millefolium), sheep sorrel (Rumex acetosella), common buttercup (Ranunculus acris), ox-eye daisy (Leucan-themum vulgare , formerly named Chrysanthemum leucanthemum), and most of the hawkweeds (Hieracium species).


Berries

You may notice that many Maine islands have an abundance of plants that produce edible fruits. The first to ripen are wild strawberries in late June. Wild Maine strawberries are much smaller than the grocery store variety but much finer! Later in July and August blueberries abound. You may find the lowbush blueberry (Vaccinium angustifolium) or the velvet-leaf blueberry (Vaccinium mytilloides). Take a close look at the leaves. If they are glabrous, meaning having no hairs, you are eating lowbush blueberry. If the leaves are pubescent, meaning with hairs, you are eating velvet-leaf blueberry. Both have delicious fruit. In August you might find ripe raspberries or blackberries, both in the rose family, genus Rubus. Raspberries and blackberries have compound leaves made up of smaller leaflets. Raspberry leaves are tomentose, meaning they have numerous gray hairs that make the leaf look whitened on the underside, whereas blackberry leaves are glabrous and appear green on the underside. There are actually a number of different species of blackberries that grow in Maine but they are hard to distinguish from each other.

In fall cranberries take center stage. Maine has three species of cranberries and sometimes all of them can be found on a single island! The mountain cranberry, or lingonberry (Vaccinium vitis-idaea ssp. minus) is a small low-growing plant with lustrous evergreen leaves roughly one centimeter long and a small, shiny, bright-red berry. It can be found in a variety of habitats, especially along forest edges and in small clearings, and it tolerates growing in drier soils. Vaccinium macrocarpon, the large-fruited or "Ocean Spray" cranberry, as I like to call it, is quite common on islands in wet places. It is easy to identify in the fall because of its ripening fruit. Earlier, in June, you might see its little, pale-pink, cup-shaped flowers. The bog cranberry, or small cranberry, also grows in wet areas and has long trailing stems and tiny involute (rolled in) leaves that appear triangular. Its fruits are slightly smaller than Vaccinium macrocarpon.


Grasses and Beach Plants

About a quarter of the plants that you will see appear "grass-like." The amateur would probably call all of these grasses, but in fact some are sedges and some are rushes. Here is a little rhyme to help tell the three apart: "sedges have edges, rushes are round, and grasses have joints." Sedges usually have a triangular stem, rushes have round stems, and grasses have a jointed stem. Many sedges, grasses and rushes inhabit wet areas. All of them have flowers; they just aren't showy. Take a closer look and you will be amazed at the diversity of these wind-pollinated wildflowers!

On most island beaches you are likely to find beach pea (Lathyrus japonicus). Beach pea has a typical pea compound leaf with tendrils on the tips, pink to purple flowers, and supposedly edible pea pods, though I have never tried them. If you are on a cobble beach you may be lucky and find the unusual Mertensia maritima, which is more common in the Canadian maritimes and Greenland than it is in Maine. Known as seaside lungwort, seaside bluebell, or oysterleaf for its fleshy blue-gray leaves, this plant has bluish bell-shaped flowers and is a relative of the Virginia bluebell. It is easy to identify even without flowers because of its unusual gray-colored foliage.


The Intertidal Zone

In the intertidal zone, where plants are covered regularly with salt water, you are likely to see fleshy-leaved "halophytes" such as goose tongue (Plantago maritma var. juncoides), also called seaside plantain. This native plantain is a relative of the common Eurasian plantain (Plantago major), a pesky lawn weed with rounded leaves which most everyone has seen at some point. The glassworts or samphires, Salicornia species, are often found in intertidal areas with muddy or fine-grained substrates. Salicornia depressa is the most common glasswort in Maine. The whole plant is green to reddish and sometimes appears translucent in the fall. The stems and leaves are hardly distinguishable from each other at first glance. The plant looks like a water balloon creature shrunk into a minute tree-like form. The stems and branches are filled with fresh water as a reserve to sustain it amidst abundant salt water inundations. The opposite leaves are reduced to tiny scales visible along the stems. And believe it or not these plants have flowers! You have to look very carefully to see the flowers' minute anthers, the pollen-bearing structures, protruding from the branches.

The diminutive sea milkwort (Glaux maritima) is my favorite of these halophytes, but not as common as the others I've mentioned. It is a low-growing, fleshy-leaved plant which is usually found in mats and has small whitish-pink flowers when in bloom. Another interesting plant in this often wet, saline habitat is silverweed (Argentina anserina, formerly named Potentilla anserina), which is easy to spot with its bright yellow flowers in July and zigzag leaf margins. The underside of the leaves are tomentose and thus appear silver, giving the plant its common name. Late in summer and early fall, sea lavender (Limonium carolinianum), a relative of ordinary garden statice, blooms. It has tiny purple flowers. The stalks are often harvested and dried for use in wreaths, which unfortunately can deplete wild populations of the plant. Many garden varieties exist that can be grown and then dried to serve the same purpose, yet won't impact natural populations.


Ferns

You will undoubtedly find many ferns, an interesting group of spore-producing plants, in your travels. They thrive in cool, moist, shaded areas, which are common on Maine islands. Some of the easier-to-recognize ferns are species of rock polypody (Polypodium virginianum and P. appalachianum) which appear almost identical, and are often found growing in leaf litter duff on top of large rocks. The fronds are singular and look like they are growing in a small colony or mat. If you turn one of the fronds over you may see the kidney-shaped sori, clusters of spore-producing structures, on the underside. Another pair of related common island ferns are cinnamon fern (Osmunda cinnamomea) and interrupted fern (Osmunda claytoniana) . These two also look very much alike. Both are large ferns with non-fertile (vegetative) fronds arranged in whorls around the center. Cinnamon fern has separate, fertile, spore-producing fronds which sprout from the center of the plant in spring. These fronds are a cinammon-like golden brown in color, which surely accounts for the plant's common name. Interrupted fern produces fertile leaflets in the upper third of the vegetative fronds, hence the frond is "interrupted" by the smaller fertile leaflets "within" the frond. Once you see this it will make sense!


Bog Mosses

If you find a bog on your island you are sure to see Sphagnum (pronounced "sfagnum") moss. Mosses, like ferns, reproduce by spores. However, mosses don't have well developed conductive tissue and therefore cannot move water and nutrients throughout their systems as effectively as ferns and other vascular plants. Because of this, mosses by necessity always grow in low mats in wet areas close to their nutrient source. Sphagnum species are common and come in shades of green, red and brown. Bog hummocks, which are small mounds of Sphagnum , often form to create an undulating bog surface. Each species of Sphagnum finds its own niche based on levels of soil moisture. Therefore, the species of Sphagnum growing on the top of the hummocks are usually different from the ones growing between the hummocks!


Woodland Flowers

If you are on a wooded island, look for common, native woodland flowers, such as wild lily-of-the-valley (Maianthemum canadense), bunchberry (Cornus canadensis) , goldthread (Coptis triflora formerly C. groenlandica), bluebead lily (Clintonia borealis), and starflower (Trientalis borealis). Bunchberry is a member of the dogwood family and has dogwood-like white flowers in spring and red "bunch"-berries later in the season. Notice the arcuate venation-arching veins-on its leaves, a hallmark of the dogwood family (Cornaceae) . Bluebead lily has a pale yellow flower in spring and later a striking blue fruit which is poisonous. Goldthread gets its common name from its golden thread-like roots. You can take a peek at the gold threads without harm to the plant by carefully pulling the soil or moss away from the roots and then pushing it back. You are likely to find bayberry shrubs at the edge of forested areas and oftentimes at the upper end of beaches. Bayberry leaves are a shiny deep green and have a lovely scent that inspires the popular bayberry candles.

In August and September our native wildflowers, the asters and goldenrods, both in the aster family (Asteraceae formerly named Compositae), are in full bloom. Their European relatives, daisies and black-eyed susans, are also in this family. Each "flower" is a composite made up of many disk and ray flowers. Disk flowers are in the middle surrounded by ray flowers. Each "she loves me, she loves me not"petal is actually a complete flower (take a look with a hand lens). So what appears to be one aster or daisy flower is made up of many disk and ray flowers fused together. If you look very carefully at goldenrods you will see that they too are made up of tiny daisy-like "flowers."

If you are interested in identifying island plants, I recommend bringing a wildflower, tree, fern, or flora guide. I personally like Newcomb's Wildflower Guide , and I especially recommend it for beginners, because it has easy identification keys and great drawings. However, plenty of excellent field guides exist and it is really a personal choice as to which one you like best. For the serious botanist a copy of the Flora of Maine with its excellent dichotomous keys (no pictures!) is a must (visit www.vfthomas.com on the web). The Flora of New Brunswick , with black and white sketches of most plants, works well for Maine and is available in a second printing (visit www.unb.ca/departs/science/biology/Flora.html). Another handy tool is a small magnifier or hand lens to look more closely into what you find. Remember to always leave plants where you find them and do not trample vegetation. Savor these special places, explore their diversity, and enjoy island plants in their wild home.

Linda Gregory is a botanist at Acadia National Park.