Starry rosinweed is a relatively short rosinweed that grows scattered mostly in the southern half of Missouri, mostly in the Ozarks. It blooms May through September.
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.
The flowerheads are loose, open clusters at the top of the plant, usually with 13–17 yellow rays that are 1/2–1¼ inch long.
Blooms May–September.
The stems and leaves are roughened and hairy, but the leaves are not leathery.
The leaves mostly alternate. The 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 margins may be toothed or untoothed). The leaves become smaller at the top of the stem and have progressively shorter leaf stalks and the blades have progressively less tapered bases, with no teeth.
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 rough but not leathery, become gradually smaller, and have gradually shorter leaf stalks, higher on the stem.
Similar species: Six Silphium species are recorded for Missouri. Of these, starry rosinweed, prairie dock (S. terebinthinaceum), wholeleaf 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.
To separate rosinweeds from the similar-looking sunflowers (genus Helianthus), see Ecosystem Connections.
Height: usually 1 to 3 feet, but can reach 5 feet.
Scattered, mostly in the Ozarks. Missouri is on the northwest edge of this plant’s overall range.
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.
Status
Native Missouri wildflower.
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
Many bees, butterflies, and other insects visit and pollinate the flowers.
Plant-insect interactions are a fertile area of study and are at the heart of how food chains work. 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!
Starry rosinweed and other rosinweeds are in their own genus, Silphium, and not in genus Helianthus (sunflowers). Yet the two groups look so much alike! How can you tell the difference? It has to do with which parts of the compound flowerheads produce seeds:
- The disk (center) florets in rosinweeds are staminate (male, producing only pollen) and therefore don’t create seeds; meanwhile, the disk florets in sunflowers are pistillate and create seeds. Then, in rosinweeds, it’s the petal-like ray florets that are pistillate (female) and turn into seeds, while those in sunflowers produce only pollen.
- Due to the above fact, the disks in rosinweeds tend to be smaller in diameter than the disks of sunflowers.
- Looking beneath the flowerhead, the green, leafy outer involucral bracts in rosinweeds are comparatively large and broad compared to those in sunflowers.
