Starry Rosinweed

Silphium asteriscus

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Photo of starry rosinweed flowerheads on a black background
Compared to Missouri's other rosinweeds (in genus Silphium), starry rosinweed has the fewest petal-like ray flowers.
Jim Rathert
Family

Asteraceae (daisies, sunflowers)

Description

Starry rosinweed is an upright perennial herb with short, stout rhizomes. The stalk is usually solitary (though in colonies they can appear clustered) and usually branch only at the top of the stalk as flowerheads form. Flowerheads loose, open clusters at the top of the plant, with 15–21 yellow rays. Blooms May–September. Stems and leaves are roughened and hairy, but the leaves are not leathery. Leaves mostly alternate. Lower leaves, which have often withered away by bloom time, have long petioles and are elliptic to narrowly ovate to lanceolate, unlobed, tapered at the base and tapering to a usually sharp-pointed tip. The leaves become smaller at the top of the stem and have progressively shorter leaf stalks and have progressively less tapered bases.

Similar species: There are 6 Silphium species recorded for Missouri. Of these, starry rosinweed, prairie dock (S. terebinthinaceum), rosinweed (S. integrifolium), compass plant (S. laciniatum), and cup plant (S. perfoliatum) are relatively common. The sixth species, rough-leaved rosinweed (S. radula), is known only from a single collection from Vernon County in 1965.

Rosinweeds (genus Silphium) generally resemble sunflowers (genus Helianthus). But here’s a big difference: The disk (center) florets in rosinweeds are essentially staminate (male) and therefore don’t create seeds, just pollen; but the disk florets in sunflowers, as most of us know, create seeds. In rosinweeds, it’s the petal-like ray florets that are pistillate (female) and turn into seeds, while those in sunflowers produce only pollen.

Key Identifiers

 

  • Stems and leaves are hairy and roughened.
  • Typically only has 13–17 ray florets, though there may be as few as 8 and as many as 20. Most of Missouri's other rosinweeds usually have at least about 20.
  • Usually only reaches about 3 feet in height.
  • Branches only at the top.
  • Leaves become gradually smaller, and have gradually shorter leaf stalks, higher on the stem.
Size

Height: usually 1 to 3 feet, but can reach 5 feet.

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Photo of a starry rosinweed plant in bloom
Starry Rosinweed
Starry rosinweed is a relatively short rosinweed that grows scattered mostly in the southern half of Missouri. It blooms May through September.

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Closeup photo of starry rosinweed immature flowerheads
Starry Rosinweed Developing Flowerheads
Starry rosinweed is a rough, hairy plant that grows on glades, blufftops, upland forests, and in pastures and roadsides.
Habitat and conservation

Occurs in glades, tops of bluffs, sinkholes, and openings of dry upland forests; also occurs in pastures and ditches and along railroads and roadsides.

Distribution in Missouri

Scattered, mostly in the Ozarks. Missouri is on the northwest edge of this plant’s overall range.

Human connections

Starry rosinweed isn’t the most breathtaking member of its genus, but it contributes to the legions of sunshiny yellow composite flowers that adorn our Ozark hills in midsummer.

Rosinweeds exude a gummy resin when cut (hence the name), and Native Americans and pioneers used this exudate as a kind of chewing gum. Most species had folk medicinal uses, too — for example, for pain relief or for treating urinary tract infections.

Ecosystem connections

Plant-insect interactions are a fertile area of study. Researchers in Illinois found that several types of insects spend most of their lives within the stems of certain types of rosinweeds. They found that certain species of tiny wasps (genus Antistrophus) are so connected to specific types of rosinweeds that their survival depends on being able to deposit their eggs in the stems of these species. In response, the rosinweed develops a swollen-looking gall around the larvae. The larval wasps feed on a specialized lining of nutritious cells within their chamber before maturing and exiting their natal home. In a fascinating twist, other types of wasps deposit their eggs into existing stem galls, and their larvae parasitize the larvae of the Antistrophus wasps. Complicating the situation further, those secondary wasps may themselves be parasitized by yet other wasps!