Featured Plant

July

Lyonothamnus floribundus subsp. aspleniifolius

Scientific name: Lyonothamnus floribundus subsp. aspleniifolius

Family: Rosaceae

Plant type: Large evergreen tree

Environment: Full sun, well-drained soil, drought tolerant

Bloom: Clusters of small white flowers

Uses: Screening plant

About

Lyonothamnus floribundus subsp. aspleniifolius

The Santa Cruz Island ironwood (Lyonothamnus floribundus subsp. aspleniifolius) is a large, evergreen tree native to the Channel Islands off the central coast of California. Of the five islands that make up this unique island chain, the Santa Cruz Island ironwood is found on three islands: Santa Cruz, San Clemente, and Santa Rosa. On the islands these trees are found in canyons, ravines, ridges and rocky slopes in chaparral and oak woodlands.

The genus Lyonothamnus is monospecific, meaning that it has just one species: Lyonothamnus floribundus. The species has been split into two subspecies based on geographic distribution and markedly different leaf characteristics. Lyonothamnus floribundus subsp. aspleniifolius is one of two subspecies the other being Lyonothamnus floribundus subsp. floribundus. Lyonothamnus floribundus subsp. floribundus is found only on Catalina Island and is much less common in cultivation.

Fossil records show that the species was more widely distributed throughout California and Nevada approximately 20 million years ago when the climate was much wetter than current conditions. As the earth’s climate changed, Lyonothamnus disappeared from the mainland approximately 6 million years ago. Today, the IUCN Red List has found that native populations of Lyonothamnus floribundus subsp. aspleniifolius are vulnerable. These populations are threatened due to grazing animals on the islands, wildfires, and climate change.

The seeds of the Santa Cruz Island ironwood have also been found to have low viability. As a result, seedlings are rarely found in the wild. The groves that do exist, however, have been found to be clonal groves that developed slowly over time by sprouting from stumps of other mature individuals.

The fern leaf ironwood is popular in cultivation and was brought to the mainland by Francesco Franceschi, an Italian horticulturist focused on introducing new species to horticulture in California, in 1894. To successfully propagate individuals, he took a burl stump off Santa Cruz Island and began distributing the suckers from the stump throughout California in 1905. The subspecies grew in popularity and in 1935 the fern leaf ironwood was named the official city tree of Santa Barbara.

Today the Santa Cruz Island ironwood remains a popular specimen in cultivation. It is noted as a fast-growing tree with interesting foliage, attractive peeling bark, and small white flowers. The leaves resemble the fronds of Asplenium ferns, a characteristic that lends itself to both the common name, fern leaf ironwood, and the name of the subspecies aspleniifolius. The name ironwood refers to the strength of the wood which was so hard it could be used by sailors for handspikes, a tool similar to a crowbar today.

IN BLOOM CONTRIBUTORS: Text and photos by Victoria Stewart.