Gathering the Laurels

I grew up enjoying the site of mountain-laurel blooming in profusion each June. It is a common understory shrub in the Hudson Highlands, one of the northeast-southwest-trending chains of mountains that make up the northern Appalachians through downstate New York. Kalmia latifolia is an evergreen member of the Ericaceae (heath family), but it is definitely most noticeable when it flowers. The pink-tinged white blossoms are arranged in corymbs; the petals are attached to form pentangular bowls. The corymbs are several inches across; each flower is about an three-quarters to an inch in diameter. It is a showy plant.

Mountain-laurel in flower in Maryland.
Mountain-laurel in flower in Maryland.

In addition to their large size, the flowers are set against glossy, dark green foliage. K. latifolia has the tendency to form large, continuous thickets, sometimes covering part of an acre on rocky, well drained hillsides. In the southern Appalachians, they can attain the size of a small tree (over 20 feet tall), but in the northeastern states they are usually five or six feet tall.

I haven’t seen any mountain-laurel on Martha’s Vineyard yet, but it does occur here and is likely to be found “up-island” in the towns of West Tisbury, Chilmark, and Aquinnah. The Gay Head and Martha’s Vineyard Moraines create a series of northeast-southwest-trending ridges that form the upland portion of the island. The terrain is dotted with large boulders (especially in the Gay Head Moraine areas) and was apparently originally forested with more beeches and maples (Northern Hardwood assemblage), tempering the dominant Oak-Heath presence that still dominates the down-island portion of the island, which a sandy outwash plain formed by the erosion of the moraine.

Sheep-laurel. (Photo: Bob Cunningham)
Sheep-laurel. (Photo: Bob Cunningham)

The most common member of the heath family in the outwash plain is the sheep-laurel, Kalmia angustifolia. This is a much smaller plant than K. latifolia, getting only about three feet all, but it has the same tendency to grow in extensive thickets. It is a common part of the Oak-Heath assemblage wherever it is found. It has evergreen leaves that hang down at a sharp angle. As its trivial name implies, the leaves of sheep laurel are narrow. It can also be distinguished from other Kalmia species because its branches end in terminal whorls of leaves, while the flowers emerge from the stem beneath the terminal leaves. The flowers resemble those of mountain laurel, but are a deep pink and much smaller.

The third member of the genus that is found in the northeastern U.S. is Kalmia polifolia, the bog-laurel. While the other two species are associated with mesic or even dry habitats, K. polifolia lives up to its name and is strongly associated with hydric conditions, although not necessarily bogs. K. polifolia is distinguished from K. angustifolia by the position of its flowers, which are terminal rather than growing further down the stem like the sheep-laurel’s. K. polifolia also blooms in the spring (April or May) rather than in the early summer.

Bog-laurel
Bog-laurel

All Kalmia prefer acidic soil conditions. But while sheep-laurel grows on a variety of sites ranging from wet sphagnum bogs to dry jack pine forests, bog-laurel is confined to wetlands (it is also called “swamp-laurel”). Mountain-laurel, on the other hand, prefers drier sites, but can tolerate moist soils at the edges of wetlands. While the sheep-laurel is widespread on Martha’s Vineyard, the bog-laurel is not found here at all.

The fourth member of the heath family found in the Northeast is Kalmia procumbens, the alpine-azalea, but as its name suggests, it is confined to the tundra-like areas on the higher peaks of New Hampshire and Maine and grows to be only 4 inches tall.

All parts of all members of the genus are poisonous to many mammals. The sheep-laurel gets its name for its morbid effect on that species, but the plant is poisonous to all livestock, as well as to humans. Some mammals, caribou for example, can tolerate it, and many birds depend on the fruits for winter forage.

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Coping With Too Much Water

The earliest plants were aquatic and likely evolved from green algae in the Cambrian Period, but the modern aquatic plants are land plants that have returned to an aquatic environment. Plants had to acquire many features in order to live on land, including a protective sheath to prevent them from drying out and specialized tissues to carry water and nutrients from the roots and leaves to the rest of the plant.

The first land plants were mosses and liverworts.
The first land plants were mosses and liverworts.

Returning to the water meant in some case losing some of the features and specialized cell types that they had acquired for sub-aerial life, or at least redistributing those features. In addition, they had to further evolve, developing new cell types and new morphologies to survive in the relatively low oxygen and low carbon dioxide environment under water.

The most completely aquatic plants live entirely submerged below the waterline. These are the most altered from their terrestrial ancestors. Land plants evolved rigid cells to enable them to stand up above the ground’s surface. Submerged plants are held up by the water. They also lack the cuticle that enables land plants to retain water and all of the plants’ cells seem able to absorb water, nutrients, and dissolved gases from the enveloping water.

The highly dissected leaves of Eurasion milfoil, an invasive species in the U.S.
The highly dissected leaves of Eurasion milfoil, an invasive species in the U.S.

Many submerged plant species have high dissected leaves (having a lacey pattern) or they are long, narrow and undivided. Dissection maximizes the amount surface area exposed to the environment and is essentially the opposite of what is seen in plants adapted xeric environments (e.g. cactuses).

These plants also have air-filled internal cavities where gasses can be stored and serve as interior atmospheres.

There are two classes of emergent aquatic plants: those with leaves that float on the surface and those that hold their leaves above the surface.

The most familiar example of the first are the water lilies. Lily “pads” have choroloplasts and stomata only on the top side, where sunlight can be absorbed and gas exchange can take place. This surface also has a waxy cuticle to prevent excessive evaporation. The leaves often have air cavities that serve as flotation devices.

The fragrant water lily.
The fragrant water lily.

Water lilies are an example of rooted floating plants. The roots serve large as a anchors and absorb little nutrition from the pond muck.

The other type of floating plant has no connection to the bottom at all. Duckweed is probably the most familiar example. These tiny vascular plants are so small that they are often mistaken for algae. Like algae they often produce asexually, with new leaves budding around the margins of the original one.

Finally there are the aquatic plants that are rooted in the water or at least saturated soil, but nearly all of the plant is sub-aerial. Cattails and reeds are familiar examples. These plants may be even tougher than the average land plant, having very rigid structure in order to withstand the occasional pounding they get from high water and storms.

Cattails around a retention pond.
Cattails around a retention pond.

In a wetland that includes open water, you will observe a zonation of aquatic plants with fully emergent plants like cattails at the shoreline, emergent plants in the shallow off-shore region and submerged plants in deeper water. The succession is called the hydrosere.

Eventually the water becomes too deep to allow rooted plants to send leaves up to a depth with enough sunlight to sustain photosynthesis. In some lakes where exotic species have been introduced, clarification of the water column by filter-feeding organisms like zebra mussels has allowed submerged plants to grow in deeper water than was formerly possible. Generally submerged plants can grow in water up to 3 meters (~10 feet) deep.

If you mind jumps to a marine setting like the kelp forests of coastal California, remember that kelp and all “sea weeds” are algaes and not vascular plants per se, which are much less common in saline and brackish environments.

The Winter Berry

My brother and sister are both active in local campaigns to restore the creek watersheds of suburban Maryland. Consequently my brother knows the landscape and the forest communities along those creeks pretty well. There are a number of parks along these waterways, and walkways wind through most of them. 

Ilex opaca
Ilex opaca

I was in Silver Spring for Easter earlier this year and when my brother took me for a walk he pointed out to me all the American holly. Ilex opaca is an evergreen shrub with leaves and red berries that very much resemble those of the European holly (Ilex aquifolium), but the leaves are less deeply green and not quite as shiny.

Apparently when the Pilgrims landed on Cape Cod (before the whole Plymouth Rock thing) they were delighted to see the familiar holly growing. This is the very northern limit of its range in the eastern United States and it grows only in isolated pockets through coastal Connecticut and Massachusetts. It becomes progressively more abundant southward in its range, until by the time you are walking around in suburban Maryland you are never quite out of sight of a holly shrub.

There probably should be a name for the phenomenon of seeing a plant that is familiar as a decoration or a food growing out in the landscape for the first time. You have this sort of ‘aha’ moment where you make the connection between the abstracted object and the fact that it is a living organic thing with it’s “own life” somewhere, so to speak. I felt that way upon seeing bananas growing in the Bahamas at age 12. At age 23, on my only visit to Hawaii I drove past fields of pineapples. I think I was out in the woods in Denmark the first time I saw mistletoe growing on a tree. It was a little less thrilling to see eucalyptus growing in California, because it is an invasive exotic there.

Ilex aquifolium
Ilex aquifolium

We had two large holly trees in our yard in Beacon. They were probably I. aquifolium or some cultivar thereof. Those two tree taught me the meaning of “dioecious,” literally “two houses.” It indicates a species in which the male and female flowers grow on separate plants. The females flowers are fertilized and produce fruit, so in the holly those classic red berries are only found on the female shrubs or trees. At Spy Hill one of our hollies was male and the other female. They had been planted about 10 or 15 feet from each other, a bit like the “husband and wife” trees that 19th century settlers in the Midwest once planted at each corner of their new homes.

Although I. opaca is not found in the northern United States I. verticillata is quite common. I was introduced to the “winterberry” while I was working at the Wetland Mapping Unit in the forestry department at UMass, Amherst.

This deciduous shrub is a wetland indicator according to the U.S. Fish and Wildife criteria. Interestingly it is not a “wetland obligate,” which would me that it required “wet feet.” Rather it seems to thrive in marginal habitats where other shrubs have a difficult time. Consequently it is found in both wetlands and in dry, sandy areas.

Ilex verticillata as a landscape plant.
Ilex verticillata as a landscape plant.

I. verticillata is also a popular landscaping shrub because of the densely packed red berries that cluster along the many stems that characterize its growth habit. When the leaves fall off in the autumn you are left with sprays of color to break up the monotony of your winter garden. It is popular enough so that several cultivars have been produced.

I. aquifolium is the only non-coniferous evergreen in Europe. That may be one reason why it was significant to the pagan tribal people. According to some dodgy sources of Celtic mythology, the “Holly King” and the “Oak King” were twins. There relatively power alternated through the seasons. When the oak leaves fell in the autumn the hollies would suddenly be a much more prominent presence on the landscape. And then when the spring arrived the holly would gradually be eclipsed.

This was, indeed, why I noticed the American holly in Maryland. I visited in April, before the deciduous trees had leafed out. The hollies are understory trees at best and usually shrubs 6 or 8 feet tall. Most of their berries had been eaten over the winter by birds, but their dense, green foliage stood out against the bare trunks of the oaks, basswoods, and tulip trees of the Maryland riverine forests. If I had taken a walk two months later through the same creek valley, I might never have noticed them.