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Black-eyed Susan (Rudbeckia hirta)

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Summary

An annual, biennial, or short-lived perennial. One of several species bearing the name Black-eyed Susan. Native to a wide range across North America, mostly in the Eastern half of the continent.

Range - Expand

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Native

This tentative map is based on the FHWA's ERA. This data lacks information on Canada, but also overestimates native ranges, especially around the edges, as this post explains. We have not yet reviewed or fixed this map.

USDA Plants Profile for Rudbeckia hirta

Illinois Wildflowers Page for Rudbeckia hirta

Description & Identification

To 1m (3.2') tall, usually shorter. Branches occasionally, usually near the base, with each stem.

Very similar in appearance to Rudbeckia fulgida; identification is compounded by different varieties and wide variation in both species. R. hirta is usually more consistently hairy, with stiff hairs, usually has lighter-green foliage, and prefers sunnier, drier conditions. R. fulgida is rhizomatous, whereas R. hirta is not.

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Life Cycle

Rudbeckia hirta is an opportunistic plant, altering its life cycle considerably in response to different conditions. Many sources list it as a "biennial or annual" but it does not reliably follow a predictable lifecycle the way some biennials do. It can bloom in the first year, often dying after a single season, but it can also persist for more than two years. As a perennial, it is usually short-lived. Survival of plants after blooming is influenced by heat and moisture.

Seeds require considerable direct sunlight and exposed conditions to germinate; this plant often thrives in disturbed areas, such as after fire or mowing. Able to survive repeated mowing or cutting to the ground, but not usually able to flower or set seed in regularly-mowed lawns. Often favored by periodic mowing regimes, especially if spaced so as to allow flowering and setting of seed.

Bloom time is highly variable, with most blooms from early to mid summer, but many plants continuing to bloom into fall. Some plants adopt the risky strategy of blooming as temperatures fall when the risk of hard frost approaches and pollinators are more scarce.

Basal rosettes of first-year plants or older plants that have persisted after blooming are often evergreen, especially in milder winters.

Uses

R. hirta seeds are frequently included in wildflower mixes because of its ease of germination, attractive blooms, and tendency to thrive in disturbed areas.

Sometimes cultivated in gardens, although less frequently than R. fulgida. Some cultivars exist, including ones with orange or red patterns towards the center of rays.

There are numerous Rudbeckia species native to North America, many of which overlap in range with R. hirta. Of these, R. fulgida, R. triloba, and R. laciniata have the widest range and are the most abundant in most areas.

R. hirta is very similar visually. R. triloba is somewhat similar but usually easily distinguished by its lobed leaves and smaller flowers. R. laciniata looks very distinct.

R. subtomentosa, locally common from Illinois and Missouri south to Louisiana, also has a similar flower, but grows much taller.

This 2000 phylogenetic analysis placed R. triloba and R. fulgida, as one might expect, as the closest-related to R. hirta of the common species. It also placed the Dracopsis genus in the same clade as Rudbeckia. After these, Ratibida was the next most closely-related genus. There is some uncertainty as to the relationships of other species, but other closely-related genera include Acmella, Ambrosia (Ragweeds), Echinacea (Purple coneflower), Helianthus (Sunflowers), Heliopsis ("False" sunflowers), Philactis, Salmea, Sanvitalia, Trichocoryne, and Zinnia. Most of these plants have showy flowers and are easily recognized as close relatives, but Ambrosia has wind-pollinated flowers and looks quite distinct.

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