ROSINWEED
Silphium integrifolium
SUNFLOWER FAMILY (Asteraceae)
Identification
- Flowering time - June, July, August
- Common in some prairies at NW
- Opposite, stalkless undivided leaves
- Priminent oval bracts with pointed tips at base of flower
- See comments for comparison with other "flat-headed" sunflowers
This native perennial has an erect, stout stem 2-6 feet tall. Oval to elliptic, stalkless or clasping leaves are opposite, and the upper leaf surface feels rough, much like fine sandpaper (B). Several 2-3 inch flower heads arise from the top of the plant (C). Prominent, oval, green leaf-like bracts with pointed tips surround the base of the flower which has from 21-34 petal-like, yellow ray florets (A,D). Flat disks may be greenish prior to emergence of the yellow disk florets. Unlike most sunflowers, Silphiums have fertile, seed-producing ray florets and infertile disk florets. The fruit is a flat, round seed oriented horizontal to the radius of the disk (E), a characteristic also different from the vertical arrangement of “typical” sunflowers with seed-producing disk florets.
Found in moister prairie locations, flowering from late June through August. It is common in some (not all) of the prairie restorations at Neale Woods.
The prominent oval bracts at the base of the flower head and opposite, stalkless or clasping, undivided upper leaves (B) separate this “flathead” from other sunflowers with a flat, yellow disk including our two other Silphium species.
The stems of this plant contain a sticky resinous substance responsible for the common name. Entire-leaved and Whole-leaf Rosinweed are other common names used to distinguish it from another Silphium species, Compass Plant, which has deeply divided leaves.
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