Horsetail-tree, whistling pine, or Australian pine, is native to the shores of Southeast Asia, Australia, and several Pacific islands. It was introduced to Puerto Rico early in the 1920s and has been planted for ornament and as a wind breaker. It reaches a height of 150 feet, with a trunk 2 feet in diameter. The bark is brown, very rough and sheds in strips. The long leaves are really twigs, along which the minute whitish leaves are grouped. Male flowers are minute, but female inflorescences can be recognized by their reddish stigmas. Fruits are up to three-quarters on an inch in diameter, each segment opens to release a minute winged seed. It flowers and produces fruits throughout the year. The generic name derives from the resemblance between the twigs and the feathers of the cassowary, an Australian bird similar to an ostrich. The species name refers to the resemblance of the twigs to a horse's tail.

The photographed tree is one of two specimens planted by Henry Cowles and Severo Vélez southwest and west of the de Diego Building.

Casuarina equisetifolia (Casuarinaceae)