Description
Form: Herbaceous stems growing from a semi-woody base (subshrub).
Lifespan: Seven years or more.
Leaf retention: Deciduous.
Growth rate: Moderate.
Mature Size: 3-6' (0.9-1.8m) high and wide.
Flowers: Five oval, vivid yellow petals, and two enlarged, curved, lower stamens. The petals open wide in the morning and partially close by dusk to form a ball. No nectar is produced within the flower.
Bloom: Repeatedly, throughout summer, usually after the start of summer rains, or with irrigation.
Fruit: Slender, arced, cylindrical, green turning to brown, dried pods, 6" (15cm) long or more, containing dark brown pellet-like seeds in a single row. The pods remain attached to their stems after leaves have dropped in the fall.
Leaves: Dark green, lance-shaped, medium-sized, hairless leaflets. In dry soil, the leaflets tend to rotate their petioles (stems) so their surface is nearly vertical to the ground and sun exposure is reduced. The petioles, when rotated, can also bend so the leaflet is nearly parallel to the stalk. The leaflets of individual plants vary with respect to their aroma. Some have a distasteful smell, many others none at all.
Stems: Stiff, erect, hairless, green, drying to brown in the fall. Extrafloral nectaries (nectar-producing glands) are located along the stems, near flower clusters and leaves, to attract ants.
Roots: Nitrogen-fixing*, with a taproot.
Wildlife: The plant attracts several species of sulphur butterflies, ants, and lizards searching for ants. Female sulphur butterflies investigate this plant as a potential caterpillar food plant, and seem attracted to the aroma given off by the leaflets. Butterfly eggs and larvae are seldom seen, however, when ants are nearby.
Ants pollinate the flowers and guard against other insects that attack plants. Gardeners should note, however, that harvester ants are known to cut off some leaflets of this plant, when it is near to their nest, and is watered during a drought.
Toxic / Danger: There are no reports of toxicity specifically concerning this plant, Senna hirsuta v. glaberrima.
Origin: Arizona, New Mexico, and Northern Mexico for this variety. South America for most Senna hirsuta varieties.

Cultivation and Uses
USDA hardiness zones: 8-9. This wildflower dies to the ground in winter, leaving dry brown stalks and persistent seed pods. It normally reappears mid to late spring but can be induced to leaf out early, with regular water, starting late winter.
Heat tolerant: Yes.
Drought tolerant: Yes.
Sun: Full sun to part shade.
Soil: Well draining, pH 6.6-7.8 (neutral to slightly alkaline). *Do not use a nitrogen fertilizer.
Water once established: Monthly. This plant tolerates frequent watering.
Prune: In winter, cut to the ground, except keep one short central stalk to mark the location of its roots.
Litter: Low.
Propagation: Seed.
Uses: Ornamental, accent plant, low water (xeriscape) garden.

Comments
This plant is a member of the Legume family (Fabaceae) and a very showy desert plant. Senna hirsuta v. glaberrima is one of seven wild varieties of Senna hirsuta, and the only variety found in the United States and northern Mexico. The name Woolly Senna is commonly used even though this variety has smooth, hairless leaves. Another common name is Slimpod Senna.

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