A Tale of Two Lupines

Sundial lupines planted by the Bar Harbor Garden Club blooming in May 2022. A similar native lupine garden was installed at the Hulls Cove Visitor Center in November of 2022.

Bar Harbor Garden Club

Less than a century ago, visitors wouldn’t have seen fields awash with purple flowers on a summer drive to Acadia National Park. In fact, while there are hundreds of lupine species worldwide, only one has historically been found growing wild in Maine: the sundial lupine, Lupinus perennis. The sundial lupines planted at the Hulls Cove Visitor Center by the Bar Harbor Harden Club closely resemble today’s roadside flowers, yet Maine’s native lupine species is now considered extirpated, or locally extinct. The western lupine, Lupinus polyphyllus, has taken its place. These two species may look alike but have very different stories to tell.

Left image
L. perennis, Maine's native lupine
Credit: Bruce Patterson. Used with permission.

Right image
L. polyphyllus, non-native to Maine
Credit: Marilee Lovit. Used with permission.

Native ranges of western lupine (purple) and sundial lupine (blue) according to the USDA Plants Database.

Most lupines are perennial plants with tall spikes made up of many flowers. Their whorled, palmately compound leaves are distinctive--you might say the leaf looks like a sundial, with leaflets pointing out from the center like the hands of a clock. Lupines and other plants of the legume family (Fabaceae) produce seed pods but quickly spread via root shoots as well. This family also shares a symbiotic relationship with bacteria that convert nitrogen in the air to a form that plants can absorb from the soil. Nitrogen fixation is the reason behind planting beans as a garden companion (or introducing the notorious invasive plant kudzu to prevent erosion). Lupines grow well in nutrient poor gravelly soil of fields, meadows, roadsides, and cleared rights-of-way.

The sundial lupine supports a variety of pollinators. The clouded sulphur, eastern tailed blue, and gray hairstreak butterflies can be found in Acadia National Park. The endangered karner blue butterfly (bottom right) has not been documented in this area.

NPS Photo/Jim Kaftan, NPS Photo, NPS Photo/Brendan Morgan, USFWS/Katie Goodwin

Each lupine species has a unique area of the world where it can survive; it may or may not share its range with another lupine, but it will always be surrounded by other living things. Over millions of years, plants adapt to their surroundings and coevolve with organisms they interact with. A well-known example is the monarch butterfly’s dependence on milkweeds as a larval host, but similar relationships exist between many other plants and pollinators. Maine’s native sundial lupine was the essential food source for the increasingly rare and endangered karner blue butterfly found in southern New England. Clouded sulfur, eastern tailed blue, and gray hairstreak butterflies benefit too, as do hummingbirds and native bees. Western lupine has similar relationships with butterflies in its native Pacific Northwest, but the leaves of this species and its hybrids are toxic to karner blue caterpillars and do not serve as host in the life cycle of Acadia’s native pollinators. On the scale of millions of years, plants expanding to new areas has led to the incredible biodiversity we see today--but what happens when we speed up that timeline of introduction or alter our environment so drastically that this biodiversity is lost?

Neither species of lupine is listed in the 1894 Flora of Mount Desert Island. Published updates to the flora in 1921 and 1929 did not yet include L. polyphyllus, but it is referenced in an entomologist's specimen notes for beetles collected on “meadow rue, lupin, and the like” in July 1934.

Though sundial lupine has not been found in Acadia National Park, it was present in Maine until recent population declines. Acadia’s flora and fauna are historically well-documented, as are the elaborate gardens of the early-1900s island villages where the wealthy elite displayed plants from around the world. The 1894 Flora of Mount Desert Island comments on the abscence of plants in the same family as lupine, but that they would likely be successful once introduced.

“The Island flora contains only eighteen species [in the Fabaceae family]…obviously a very insufficient representation when we consider that shown by many points further north with otherwise much the same flora. Of these species, ten are naturalized on this continent from Europe; two are introduced from other parts of North America; two more may also have been so introduced; leaving only four species that are indigenous…When northern species of this family are introduced on the Island they flourish as well there as elsewhere.”

It is estimated that western lupine was introduced to the northeast by the 1950s, and it certainly flourishes on the island today. Colorful hybrids and cultivars of lupines thrived on the island. Western lupine’s attractive flowers and prolific growth soon carried it beyond the garden walls, along with other species that are managed by Acadia’s Invasive Plant Management Team (IPMT) today. Intentionally planted along roadsides and quick to spread on its own, western lupine eventually displaced the sundials throughout the northeast.

When L. polyphyllus first came to Mount Desert Island is not known exactly, but it spread during a period of rapid development, road construction, increased visitation, and other environmental disturbances such as the Fire of 1947. The added stressors of soil compaction and degradation on native vegetation, coupled with the western lupine’s larger size and higher tolerance for these conditions, allowed it to outcompete and crowd out other plants. This origin story is common among many invasive plant species. In parts of the Midwest and Northeast, western lupine is considered an invasive species, meaning its introduction has caused economic or environmental harm or harm to human health. In some areas, the lupine’s abundance and ability to add nutrients to the soil can significantly increase nitrogen levels beyond what native species can tolerate. Though its sale is not restricted in the state, it is included on the Maine DACF Advisory List for its invasive potential.

BHGC volunteers planting sundial lupine seeds at the Hulls Cove Visitor Center in November 2022.

Bar Harbor Garden Club

Acadia National Park's efforts to manage invasive and non-native plants began in the late 1980s with purple loosestrife, a widespread invader of wetlands. The IPMT now focuses on 25 species that create challenging conditions for Acadia’s diverse flora and fauna. With the understanding that lupines are a popular feature of the disturbed roadside landscape, NPS does not currently manage lupines unless it is for the protection of an at-risk species or encroaching into significant natural habitats, like wet meadows or mountain summits. In years past, the IPMT has removed lupines encroaching on a significant area of milkweed to protect habitat for the now-endangered monarch butterfly. While Acadia’s natural resource managers focus on high-priority invasive species, it’s worth monitoring the risk posed by western lupine and considering what could grow in its place.

On Mount Desert Island, documenting the presence of sundial lupine and its rare pollinators remains a natural history mystery. In planting sundial lupines within an approximate historical range, the BHGC hopes to share appreciation for this iconic flower, encourage the use of native plants in home gardens, and provide the far-reaching benefits of restoring native plants to Maine’s landscapes.