Family: Arecaceae
Common Name: Washingtonia Palm, Cotton Palm, Thread Palm

There are only two species in this genus of fan palms, from the south of the United States and Mexico. They are among the hardier palms and are extensively planted in California and Florida. These, tall, vigorous palms have a single, upright trunk and a fairly compact crown. The large, fan-shaped leaves are similar in width and length and are divided into drooping, strap-like segments. The leaf stalks are of moderate length and edged with spines. A most distinctive feature is the dense, gray-brown skirt of dead leaves that forms around the trunk, sometimes totally enclosing it. The long, slender inflorescences, comprised of small, delicate, white flowers, extend out well beyond the leaves and are followed by small, brown, egg-shaped fruits. Below climatic zone 9, grow in an intermediate greenhouse or con­servatory, or as a house plant.

Species

W. filifera, desert fan palm or cotton palm, occurs naturally in south-western United States and into Mexico, and is the more drought- and frost-tolerant of the two species. The stout trunk is generally up to 15 m (50 ft) tall and the crown is fairly broad and open. The huge, grayish green leaves are divided into many fine, long segments, between which long, stiff, white threads appear. These are very prominent, even from a distance, and give rise to the common name 'cotton palm'. If the dead leaves are removed as the palm grows, the trunk below will be smooth and pale gray. The long inflorescences are followed by brown to black fruits.

W. robusta, thread palm or Mexican washingtonia, is a native of western Mexico. This species is better suited to growing in the tropics, but it does not appear to like constant high humidity or year-round rainfall. It is much taller than W. filifera, with a trunk up to 25 m (80 ft) high, tapering towards the top. The glossy, mid-green leaves, borne on fairly short stalks, are less deeply cut, and form a compact crown. If the leaves are removed, the leaf bases leave a criss-cross pattern on the trunk. With this species, the white threads between the segments generally occur only on young plants. The inflorescences are smaller than those of W. filifera, but the pea-sized, dark brown fruits are borne in abundance.

Cultivation

In the greenhouse or home, grow in pots of sandy, soil-based potting compost. Ensure good light, but shade from strong, direct sun. They need only moderate watering, and should be kept only slightly moist throughout winter. In the garden, these palms need a sunny position, with well-drained soil. Propagate in spring from seed germinated at 24°C (75°F).

Climate

Warmest parts of zone 9.