Coreopsis Tickseed- Echinacea purpurea Coneflower - Eryngium yuccifolium Sea Holly- Helianthus angustifolius Swamp Sunflower - Helianthus x laetiflorus False Sunflower - Heliopsis helianthoides Ox Eye- Hemerocallis Daylily - Liatris pycnostachya Kansas Gayfeather - Liatris spicata Blazing Star, Gayfeather - Monarda fistulosa Wild Bee Balm - Ratibida pinnata Drooping Coneflower - , Gloriosa Daisy - Sedum 'Autumn Joy' - Silphium integrifolium Prairie Dock - Silphium laciniatum Compass Plant - Silphium perfoliatum Cup Plant - Solidago Goldenrod - Vernonia noveboracensis Ironweed - Yucca filamentosa Adam's Needle

Silphium perfoliatum, or cup plant is a plant that grows on prairies and gardens in the central and eastern United States. The stem is square and the leaves grow in a way that forms a cup that holds water.

http://www.illinoiswildflowers.info/prairie/plantx/cupplantx.htm

Perhaps the first known use of the heart shape comes from the 7th century BC, in Cyrene. In that city, at that time, Silphium was a plant so highly prized for it's use as birth control that it became extinct. The seeds of Silphium were shaped like hearts, however, making historians believe that the heart shape we know today was based upon this early form of birth control. Much later, the Catholic Church claimed the symbol of the heart originated with St. Margaret Marie Alacoque, who had a vision in the 17th century where she saw a heart shape surrounded by a crown of thorns.

According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern SILP----. That is, eight letter words with 1st letter S and 2nd letter I and 3rd letter L and 4th letter P. In alphabetical order, they are:

silphium