Senna armata (S. Watson) Irwin & Barneby

Spiny senna, desert senna

Spiny senna is native to the North American southwest, a shrub with a dense tangle of sharp-tipped branches. They are leafless for most of the year, so when they aren’t flowering they look like someone gathered a heap of kind­ling and forgot about it. When they are flowering, it looks like someone lit it. They are found at elevations of 328–4593′ (100–1400 m), in sandy or gravelly washes.

Plants: Shrubs up to 3′ (1 m) in height. They are densely branched, and many of the branches terminate in sharp spines. Tiny tubular hairs reflect the sun’s heat.

Leaves: Leaves are on narrow branchlets, in 2-4 opposite pairs. Each leaflet is ⅛–3/16″ (4–6 mm) around, and ovate. Leaf pairs aren’t quite symmetric. Leaves are dropped entirely most of the time, in order to conserve water.

Flowers: Yellow, or salmon pink, occurring singly or in clusters in leaf axils. Each flower has five petals, and is ⅝–⅞″ (1.6–2.4 cm) in diameter. Flower petals are not evenly distributed, so the flower has bilateral symmetry but not radial symmetry. Flowers appear from March to July.

Fruits: Pods are ⅞–1½″ (2.5–4 cm) long, straight, and con­tain a few seeds.

Habitats: Und at elevations of 328–4593′ (100–1400 m), in sandy or gravelly washes.

Similar species.

Online References:

Older scientific or horticultural names

Senna armata description by Thomas H. Kent, not updated.

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