Wholeleaf Rosinweed

Silphium integrifolium

Wholeleaf_Rosinweed_flowerheads_Friendly_Prairie_8-17-14.jpg

Photo of wholeleaf rosinweed flowerhead
Wholeleaf rosinweed looks like a sunflower, but its relatively small central disk of infertile florets reveals it as a rosinweed, genus Silphium. It occurs statewide.
Other Common Name
Rosinweed
Family

Asteraceae (daisies, sunflowers)

Description

Wholeleaf rosinweed is not quite so tall as most of our other rosinweeds and is commonly misidentified as a sunflower. Stems can be solitary or clustered and vary in their amount of hairiness, but hairs, if present, are short. The stem usually doesn’t branch except at the very top. Stems often turn reddish in bright sun. The sunflower-like flowerheads are in loose, open clusters at the top of the plant, usually with 20–35 yellow rays. Blooms July–September. Basal leaves often have withered away by flowering time. Stem leaves are thick, sometimes leathery, sometimes roughened, sometimes smooth, sometimes hairy. Leaves are usually well distributed along the stems; they are opposite, and each pair is turned 90 degrees from the pair above and below it. Stem leaves are sessile (stalkless) and become slightly smaller at the top of the plant; shape varies from lance-shaped to oval to heart-shaped to clasping, tapering to a sharply pointed tip.

Two varieties of wholeleaf rosinweed occur in our state. Var. integrifolium is a roughened, hairy plant and is scattered nearly statewide. Var. laeve is glabrous (smooth) and strongly glaucous (white-waxy coated) and is scattered along the western edge of the state, including the loess hill prairies of northwestern Missouri.

This species sometimes hybridizes with cup plant (S. perfoliatum), and where the two plants occur together, their offspring, exhibiting traits of both parents, may be present.

Similar species: There are 6 Silphium species recorded for Missouri. Of these, wholeleaf rosinweed, prairie dock (S. terebinthinaceum), starry rosinweed (S. asteriscus), 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) of the flowerheads is usually smaller than in true sunflowers. Indeed: the disk florets in rosinweeds are 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

 

  • Height usually 3–5 feet.
  • Ray florets mostly 20–35.
  • Leaves opposite, stalkless, each succeeding pair changing orientation by 90 degrees.
  • Disk of flowerhead relatively small (compared to true sunflowers); disk has staminate florets only, which do not produce seeds.
Size

Height: 16–80 inches (1 1/3 to 6 feet)

Wholeleaf_Rosinweed_involucre_Friendly_Prairie_8-17-14.jpg

Photo of the back of a wholeleaf rosinweed flowerhead
Wholeleaf Rosinweed Involucre
The receptacle beneath the flowerheads of wholeleaf rosinweed is relatively small, compared to true sunflowers.

Wholeleaf_Rosinweed_Leaves_Friendly_Prairie_8-17-14.jpg

Photo of a wholeleaf rosinweed stalk showing opposite pairs of leaves
Wholeleaf Rosinweed Stalk And Leaves
The leaves of wholeleaf rosinweed are opposite, stalkless, with each succeeding pair changing orientation by 90 degrees.

Wholeleaf_Rosinweed_7-1998.jpg

Photo of a wholeleaf rosinweed flowerhead in bloom
Wholeleaf Rosinweed
Two varieties of wholeleaf rosinweed occur in our state. The roughened, rather hairy form occurs statewide, while a smooth, waxy-coated form grows in our westernmost counties.

Wholeleaf_Rosinweed_Friendly_Prairie_8-17-14.jpg

Photo of wholeleaf rosinweed blooming at Friendly Prairie
Wholeleaf Rosinweed At Friendly Prairie
Wholeleaf rosinweed usually occurs on prairies and other sunny areas. Where it grows in bright sun, the stems often become reddish tinged.

Wholeleaf_Rosinweed_on_prairie_July_2000.jpg

Photo of wholeleaf rosinweed colony growing on a prairie
Wholeleaf Rosinweed
With the many insects and other animals it attracts, a colony of rosinweed becomes a kind of microhabitat on a prairie.

Wholeleaf_Rosinweed_colony_7-1998.jpg

Photo of a wholeleaf rosinweed colony
Wholeleaf Rosinweed
Wholeleaf rosinweed is not quite so tall as most of our other rosinweeds and is commonly misidentified as a sunflower.

Wholeleaf_Rosinweed_plant_7-1998.jpg

Photo of a wholeleaf rosinweed plant
Wholeleaf Rosinweed
The sunflower-like flowerheads of wholeleaf rosinweed are in loose, open clusters at the top of the plant, usually with 20–35 yellow rays.
Habitat and conservation

Occurs in upland prairies, loess hill prairies, openings of mesic to dry upland forests, savannas, tops of bluffs, glades, banks of streams and rivers, and rarely margins of ponds and lakes; also occurs in pastures, edges of crop fields, ditches, railroads, and roadsides.

Distribution in Missouri

Scattered nearly statewide.

Status

Usually this species is called simply “rosinweed.” Considering that the term applies to all the plants in the genus, including five common Missouri species, it emphasizes the usefulness and clarity of scientific names. The “integri” of the species name “integrifolium” denotes completeness and entirety, referring to the plant’s entire (undivided) leaves, which is one of its notable characteristics. Translating the scientific name to “wholeleaf rosinweed” helps distinguish the plant in lay terms.

Human connections

Wholeleaf rosinweed contributes to the legions of sunshiny yellow composite flowers that adorn our state in midsummer.

This is a rather coarse plant, but the flowers are showy and it is a hardy, drought-tolerant addition to a natural landscape or as a backdrop to a perennial garden.

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

Butterflies, bees, and many other insects are attracted to the flowers, and a variety of other insects deposit eggs on or in the plants, and their developing larvae eat the leaves or bore into the stalks. The presence of herbivores, pollinators, and nectar eaters attract crab spiders, parasitic wasps, robber flies, and other insect predators, creating a micro habitat right on the plant.

Birds such as goldfinches eat the seeds, and grazing animals such as deer and cattle eat the foliage.

On native prairies, most of the plants have tough taproots that often penetrate deep into the soil. Over the centuries, the living and dying of these plants caused the deep soils of the Great Plains to become some of the richest in the world.