The Karner Blue, an endangered butterfly, has three scientific names: Plebejus melissa samuelis, Plebejus samuelis, and Lycaeides melissa samuelis. Its current range is found in the Eastern United States especially around the Great Lakes above 40-degrees latitude. Information is available by conducting a search using any of the above names. Most butterfly authorities treat Lycaeides melissa samuelis as a synonym. Sorting all this out was a challenge.

A graphic range map of the Karner Blue can be found here.

There are just under 900 butterfly species in the US. Even though I have a growing database of over 7000 plant-butterfly images, this butterfly was not among them. The nomenclature problem threw me off. It took over six hours of digging to identify a single plant that attracts the Karner Blue adult butterfly.

At first I queried my favorite sites for information, and then the USDA and the National Forest service. As there are four different names for this specie, the information about is a bit fractured as well. Finding BASIC information, including sorting out the nomenclature issue, took 2 hours. A quest to add additional content took another 6. My approach to the nomenclature issues facing the interaction between butterflies and plants was altered by the data-search associated with the Karner Blue.
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The Karner Blue adult will feed on:

Coreopsis
Geranium maculatum
Monarda punctata, a beebalm
Rudbeckia hirta, black-eyed Susan
Taraxacum officinale, dandelion

Monarda is native to almost every state east of Arkansas plus Texas, Oklahoma, Kansas, New Mexico, and California. The host plant is native in all of these states except Arkansas, Missouri and Tennessee.

Planting a generic assortment of native plants is not particularly helpful for the Karner Blue. It is threatened because it has exquisite tastes. It likes this short list of plants. Growing them - along with Lupine, the Karner Blue host plant - may enable caring gardeners who reside in the general vicinity of this butterfly to actually help it survive.

Both Butterflies & Moths and the Natural History museum state that Lupine is the host plant for the Karner Blue.