Cassia bicapsularis

Native to Central and South America but naturalized across the tropics, this fast-growing shrub flowers not in spring or summer like a well-behaved plant but in autumn and into early winter, hanging great loose clusters of clear, saturated yellow at the ends of arching branches, each bloom built around curved stamens that give a vaguely butterfly-like silhouette. Cloudless Sulphur and Sleepy Orange butterflies find the shrub irresistible as both nectar source and larval host, and tend to arrive in numbers when the flowers open, a fact that either delights or mildly alarms a gardener, depending on how attached one is to the foliage. The caterpillars, for the record, are a vivid chartreuse and genuinely handsome. That is the bargain on offer.

The taxonomists, characteristically, cannot agree on the name. Cassia bicapsularis appears in the older literature; current consensus leans toward Senna bicapsularis, though the debate continues in the way botanical debates do, at length, and largely among people who care deeply. Woodlanders lists the plant as Cassia here in the old tradition, without taking sides.

In zones 9 and warmer the shrub behaves as a large, fast evergreen reaching eight feet or more. In zone 8 the plant typically freezes to the ground in hard winters and returns vigorously from the roots the following spring, a perfectly acceptable arrangement that keeps the scale manageable. Site in full sun and give room. The late-season color, arriving at the exact moment most gardens have run out of options, is not easily replaced by anything else.

Note: Woodlanders also carries 'Buttercream', a pale yellow-flowered selection shared by Joann Breland of Charleston, a quieter take on the same late-season display. Both are worth knowing.