Barleria lupulina (Hop-headed Barleria)

Native to Madagascar, this shrub or subshrub grows in seasonally dry tropical habitats and has been introduced widely beyond its native range. Its narrow, dark green leaves have a reddish midrib, and the branching stems bear spines at the leaf axils. Yellow tubular flowers emerge from dense, overlapping bracts arranged in upright spikes. After flowering, dry capsules split open to release their seeds. It is naturalized in Hawaii and Florida and is invasive in parts of northern Australia, where thorny thickets displace native plants. Photographed in Colombia.