This organization began in 1979 as a concerted effort to create a list of native plants and implement legislation on behalf of native plants. It wasn’t until 1993 that membership in the group was solicited to further their mission. They advocate conservation of native plants and their habitats and promote the increased use of native plants in the landscape. They invite anyone interested in native plants to join their organization. The annual newsletter Notes is available online to all.
The Botanical Society of Western Pennsylvania is one of the oldest botanical organizations in the country. According to their website the Society, since 1886, has met, botanized, and served as a resource of knowledge on the flowers of Pennsylvania. This group invites both amateur and professional botanists into their group. They hold regular meetings with featured speakers and organize field trips. Some issues of their monthly newsletter, Wildflowers are online.
The Swamp doghobble, Eubotrys racemosa, displaying its stem of flowers, is a member of the heath family. It is a native plant growing wild in Pennsylvania and is considered a threatened species.
Wildflowers of Pennsylvania by 
Outstanding Mosses and Liverworts of Pennsylvania and Nearby States by 
Courtesy of Wikimedia Commons/H. zell
The Pennsylvania Native Plant Society supports many Demonstration Gardens by direct management or grants in order to educate the public on the use of native plants in the landscape. Please see their website for more information and locations!
In the image above the Common Milkweed, Asclepias syriaca, is a native of Pennsylvania that can be a wonderful addition to your garden because it not only looks nice but is a favorite of monarch butterflies.