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// SPECIES PROFILE · PERENNIAL · NITROGEN-FIXER · PRAIRIE

Maryland Senna

Senna marilandica

Maryland Senna is a statuesque native legume of eastern and central North America — an upright, shrub-like perennial that sends up sturdy stems 3 to 6 feet tall and crowns them in July and August with loose clusters of bright butter-yellow flowers set against handsome, pinnately compound blue-green foliage. It is a nitrogen-fixing workhorse of the tallgrass prairie and Cross Timbers ecotone, supporting a specialist guild of sulphur butterflies that use its foliage as larval food, and its extrafloral nectaries draw a constant patrol of ants and tiny wasps that help defend the plant from herbivores. In a NE Oklahoma food forest or prairie restoration, Senna marilandica is one of the most reliable structural perennials for the middle-to-back border, blending ecological function with a long season of bloom.

// QUICK FACTS
Family
Fabaceae (legume / bean family)
Life cycle
Herbaceous perennial; dies back to a woody caudex each winter
Native range
Eastern and central US — NY south to FL, west to TX, OK, KS, NE, and IA
USDA hardiness
Zones 4–9 (Tulsa = 7a/7b)
Mature size
3–6 ft tall, 2–3 ft wide; shrub-like in full sun
Bloom
July – September (NE OK)
Sun
Full sun (6+ hrs); tolerates light shade under post oaks but blooms less
Soil
Well-drained; adapts to clay, loam, and sandy-gravelly soils; pH 5.5–8.0
Water
Dry to medium; drought-tolerant once established
Wildlife
Sulphur butterfly larval host · extrafloral nectaries feed ants/wasps · bumblebee nectar
Maryland Senna (Senna marilandica) with bright yellow pea-like flowers and pinnately compound leaves
Senna marilandica in mid-summer bloom — the showy yellow flowers and fine-textured compound foliage make this one of the most ornamental native legumes. Photo: Rooted Revival.

Identification

[ field key — stem · leaf · flower · pod · habit ]

Habit & Stem

Erect, shrub-like herbaceous perennial that dies back to a woody caudex each winter and resprouts vigorously in late spring. Stems are round, glabrous to sparsely hairy, green to reddish, and typically unbranched except near the inflorescence. The plant emerges late in the season (May in Tulsa) but grows rapidly, reaching full height by early July. Its upright, vase-shaped form makes it an excellent structural anchor in prairie plantings.

Leaves

Alternate, evenly pinnately compound, 6–10 in long with 6–12 pairs of oblong leaflets. Each leaflet is 1–2.5 in long, entire-margined, with a tiny mucronate tip. The foliage is blue-green to gray-green and notably fine-textured. At the base of each leaf petiole sits a small, club-shaped extrafloral nectary — a gland that secretes sugary fluid to attract ants and parasitoid wasps that defend the plant.

Flowers

The flowers are bright butter-yellow, about 1 in across, borne in loose axillary and terminal racemes (clusters) that open progressively from the bottom up over several weeks. Each flower has 5 unequal, somewhat overlapping petals and prominent dark-brown stamens that are a key field mark. The flowers are not papilionaceous (not pea-shaped like typical Fabaceae) — the petals spread open, giving them a star-like profile that distinguishes them from true peas.

Fruit & Seed

The fruit is a flat, narrow legume pod 2–4 in long and about ¼ in wide, green at first and maturing to dark brown in late fall. The pods split open along both seams at maturity, releasing several small, flattened, dark-brown seeds. The dried pods often persist on the plant well into winter, adding subtle winter interest and rattling pleasantly in the wind. Seeds require scarification or winter stratification for reliable germination.

Habitat & Range in NE Oklahoma

Senna marilandica is native across the eastern half of the United States, from New York and New Jersey south to Florida, and westward through the Ohio and Mississippi River valleys to eastern Oklahoma, eastern Kansas, eastern Nebraska, and Texas. In NE Oklahoma it is a characteristic species of the Cross Timbers / tallgrass prairie ecotone, where it grows in open woodlands (especially under post oak and blackjack oak), prairie openings, roadsides, fence rows, and the sunny edges of bottomland forests. It is not uncommon along county roads in the Tulsa region, especially where mowing is infrequent enough to allow it to reach bloom height.

The plant shows a preference for mesic to dry-mesic sites with full sun or dappled shade. It is remarkably adaptable to soil type, growing in heavy clay, sandy loam, and rocky limestone-derived soils alike, so long as drainage is reasonably good. In the garden it is one of the easiest native legumes to establish, asking for little beyond a sunny spot and a bit of patience during its late spring emergence (it is one of the last prairie perennials to break dormancy).

Ecology & Wildlife Value

[ sulphur butterflies · extrafloral nectaries · nitrogen fixation · bee forage ]

Lepidoptera Host

Maryland Senna is a primary larval host for sulphur butterflies, a group that feeds almost exclusively on legumes in the genera Senna and Chamaechrista. The caterpillars of the cloudless sulphur (Phoebis sennae), sleepy orange (Abaeis nicippe), and little yellow (Pyrisitia lisa) all feed on S. marilandica foliage. The caterpillars are themselves camouflaged — cloudless sulphur larvae are yellow-green and nearly invisible on the leaflets. Planting a stand of native sennas is one of the most direct ways to support the full life cycle of these butterflies in a NE Oklahoma garden.

Extrafloral Nectaries & Insect Defenders

The small glands at the base of each leaf petiole are not floral nectaries — they have nothing to do with pollination. They secrete a sugary solution that attracts ants, small parasitoid wasps, and predatory bugs. These visitors, in turn, attack or deter caterpillar eggs, leaf-chewing insects, and other herbivores. It is a classic example of an indirect plant defense mediated by mutualists, and on a warm day you can watch the steady traffic of tiny defenders patrolling the foliage.

Pollinators & Nitrogen

The open, accessible flowers are worked by a wide variety of bumblebees (Bombus spp.), carpenter bees (Xylocopa), and leafcutter bees (Megachile). The flowers produce no nectar in the usual sense — bees visit primarily for the abundant pollen, which is released through pores in the anther tips (poricidal dehiscence). As a legume, S. marilandica hosts nitrogen-fixing rhizobia in root nodules and enriches soil nitrogen in the immediate root zone, making it a valuable component of prairie restorations and food forest guilds.

Seeds & Winter Interest

The dark-brown seed pods persist on the plant through winter, providing subtle structural interest in the dormant garden. A handful of seed-eating birds, including Northern cardinals and dark-eyed juncos, may pick at the pods, though Senna seeds are not a primary bird food. The real winter ecological value is the overwintering habitat the standing stems provide for beneficial insects and spiders.

Permaculture role: A medium-to-tall nitrogen-fixing perennial for full-sun guilds. Plant Maryland Senna between fruit trees or at the back of perennial beds where its height and nitrogen-fixing capacity benefit neighboring plants without shading them. Pair with shorter prairie grasses (little bluestem, sideoats grama) and mid-height forbs (purple coneflower, black-eyed susan) for a layered prairie edge.

Horticulture & Care

[ seed starting · site · soil · maintenance · companions ]

Site selection & sowing

Maryland Senna is extremely easy from seed, but the seed coat is hard and requires scarification for reliable germination. Nick the seed coat with a file or soak seeds in near-boiling water, then let them sit in the cooling water for 12–24 hours before sowing. Direct-sow in fall for natural cold stratification, or start indoors 6–8 weeks before last frost after scarification. Plants emerge late in spring (May) and grow quickly once soil warms. Pick a site with full sun for maximum bloom and structural strength; plants in partial shade will be leggier and bloom less heavily.

Soil, fertility, and maintenance

As a nitrogen-fixer, Maryland Senna needs no supplemental nitrogen fertilizer. In fact, too-rich soil produces floppy, top-heavy stems. A light topdressing of compost in fall is sufficient. The plant is clump-forming and does not spread aggressively; it can be left undisturbed for years. Cut back dead stems to 6–8 in in late winter before new growth emerges. If stems lean or flop in rich garden soil, install a grow-through ring early in the season.

Pests & diseases

Companion plants

Pairs beautifully with tall prairie grasses (switchgrass, Indian grass, big bluestem), mid-height composites (purple coneflower, black-eyed susan, rough blazing-star), and other prairie legumes (roundhead lespedeza, leadplant, purple prairie clover). The fine-textured foliage and vase-like form provide excellent contrast with the bold, broad leaves of compass plant or prairie dock. Also effective as a short hedge or screen when planted in a row at 18–24 in spacing.

Sources & Further Reading

Hero photo: Rooted Revival.