Summer may have officially ended, but there is still plenty to see in bloom around Nantucket. August through mid-October bring a roster of newly emerging late bloomers, with the fall asters and goldenrods taking center stage. These members of the Aster Family (Asteraceae, or Compositae), have flower heads that are composed of several to many small flowers packed together, often forming what appear from a distance to be individual larger flowers.
Some species have arching or vertical arrangements with florets grouped into small bundles resembling sprays of fireworks — such as goldenrods and New England blazing star (Liatris novae-angliae), while others have small florets tightly packed in a central disc, surrounded by more showy, often contrasting colored florets called ray flowers. These look to the human eye like large petals—and are found in familiar garden plants such as daisies, sunflowers, chrysanthemums, and asters.
In a botanical plot twist, one of the dominant Asteraceae species flowering in great abundance across the island in late September and early October is the large shrub species called groundsel (Baccharis halimifolia). Tall and robust, groundsel bushes are often found around salt marshes but can occur almost anywhere on our salty windy island, wherever seeds have blown and been deposited on sandy disturbed soil.
Each groundsel shrub is either male or female—you can easily tell which one as they come into bloom; the males have yellowish flowers laden with pollen, and the females quickly develop a silky white pappus that becomes quite showy against the cranberry colored bracts at the base of the flower heads. Bees and other late season insects flock to the pollen and nectar provided by the groundsel. As the season wears on, the male flowers fade from view and the female flowers continue to grow longer and longer silk, eventually drying and dispersing the parachuted seeds into the wind.
Meanwhile, seaside goldenrod (Solidago sempervirens) is putting on a golden show in the nearby dunes and upper beaches and salt marsh edges. Like groundsel, this late bloomer is very important for bees getting in their last meals of the autumn, and for migrating monarchs and other late season butterflies braving our windy skies.
What goes best with gold? Numerous asters are showing off their colors in the grasslands and low shrublands around the island, often sporting bright white, lavender, or purple ray flowers with central discs that range from pale yellow to gold and orange. A walk at Ram Pasture, Squam Farm, or Windswept Bog this time of year reveals a tapestry with several species of asters in bloom, with scattered patches of goldenrods here and there for contrast. The clear “bluebird skies” of autumn really show off this color palette on a sunny October day.
Enjoying the beauty of these native wildflowers is easy; identifying exactly which one you are looking at can be a lot more challenging. Bushy aster (Symphyotrichum dumosum) seems to be the most adaptable and widespread of the bunch on Nantucket. It’s common in drier habitats, where you can find it growing with grass leaved goldenrod (Euthamia graminifolia) and slender leaved goldenrod (Euthamia caroliniana) and New England blazing star. Bushy aster is usually white to very pale purple with a yellow center, and the upper stems have many small leaflike bracts on the stems just below the flowers.
Heath aster (Symphyotrichum ericoides), which you might expect to dominate our coastal heathlands, is actually more common along busy road edges or untended lots, where it escapes mowing and bursts into flower at the end of September. Also with white to very pale lavender flowers and yellow centers, I find it easiest to distinguish this aster by its dense clustering of flower heads, and check it up close to look at the series of green bracts enclosing the base of the flower heads. Unlike bushy aster, the bracts curve out almost at right angles and each bract has a spine tip.
At Windswept and along ditch or wetland edges elsewhere, New York Aster (Symphyotrichum novi-belgii) is also blooming profusely from late summer into October. New York aster’s flowers are more of a true lavender with yellow to orangish centers, and the individual flower heads are quite a bit larger and showier than heath aster and bushy aster. The upper stems and leaves are often a burgundy or cranberry color, and lightly hairy, while the leaves have a bit of a crease down the center formed by the midrib.
Hiding in plain sight at Windswept, another very similar species can be found with close attention to detail– smooth aster (Symphyotrichum laeve). This aster’s large showy flowerheads are about the same shade of purple and yellow as New York aster, but the upper stems only have lines of hairs or are hairless, and the leaves are flat rather than indented along the midrib as seems more common in New York aster.
Wavy aster (Symphyotricum undulatum) is also on the darker end of the “purplish aster spectrum” here on Nantucket and has distinctive leaves that help you identify it without a fuss. The upper stem leaves are heart shaped (cordate) and clasp the stem, but the lowest stem leaves are indented near the clasping part, almost as if neatly cut away to make a narrow waist. The exact shape is highly variable, but you can usually find a few of these unusual leaves near the bottom of the plant. This species seems to be having a particularly big flowering year in 2020.
There are plenty more asters and goldenrods out there to explore over the next few weeks, forming colorful oases in a sea of dry grasses and reddening foliage of the shrubs. Consider the feast of pollen and nectar these diverse late season wildflowers offer, and the many species that will feed on their abundant seeds over the winter. A close look will often reveal a microcosm of flying insects, colorful spiders lying in wait, and some visiting butterflies and moths.