Cutleaf Rosinweed, Cutleaf Prairie Dock, Tansy Rosinweed, Southern Dock - Silphium pinnatifidum
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Silphium pinnatifidum - Cutleaf Rosinweed, Cutleaf Prairie Dock, Tansy Rosinweed, Southern Dock. Rosinweeds look very similar to sunflowers, but the seeds form from the ray flowers in rosinweeds, and from the disk flowers in sunflowers. Silphium pinnatifidum can be to 10' tall, and has numerous heads on branching, nearly leafless stems. S. pinnatifidum is considered by some botanists to be a variety of S. terebinthinaceum, with the primary difference being the deeply lobed (almost to the central vein) leaves in S. pinnatifidum. The basal floret of leaves in S. terebinthinaceum are spade-like.
Found in:
AL, GA, IL, IN, KY, TN, WI
Journal Articles Referencing Rosinweed
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Distribution of Silphium pinnatifidum in the United States and Canada:
Map courtesy of The Biota of North America Program.
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| | Site: Walker County, GA Date: 2009-September-14 | Photographer: Gerald C. Williamson
Nikon D60
2 secf/16 ISO200
Tamron SP 90MM f/2.8 AF Macro
90mm (135 equiv) Flash: | | Cutleaf rosinweed may have 13-21 yellow ray flowers and numerous yellow disk flowers. | | 
| | Site: Walker County, Ga Date: 2009-September-14 | Photographer: Gerald C Williamson
Nikon D60
1.3 secf/10 ISO200
Tamron SP 90MM f/2.8 AF Macro
90mm (135 equiv) | | Each Silphium pinnatifidum blossom forms at the end of a branch, which usually arises from a clasping, greatly reduced leaf bract along the stem. | | Click on the photo for a larger image
| | Site: Walker County, Ga Date: 2009-September-14 | Photographer: Gerald C Williamson
Nikon D60
1/400f/5.0 ISO200
Tamron SP 90MM f/2.8 AF Macro
90mm (135 equiv) | | Rosinweed blossoms (genus Silphium) look very much like sunflower blossoms (genus Helianthus.) However, the seeds come from the ray flowers in Silphium, and from the disk flowers in Helianthus. | | Click on the photo for a larger image
| | Site: Walker County, Ga Date: 2009-September-14 | Photographer: Gerald C Williamson
Nikon D60
1/125f/4.0 ISO200
Tamron SP 90MM f/2.8 AF Macro
90mm (135 equiv) | | A key identifier for Silphium pinnatifidum is the basal rosette of tall, deeply lobed leaves. The leaves may be 30" or more tall, split more or less evenly between the stalk and the leaf. | | Click on the photo for a larger image
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