Lyonothamnus floribundus subsp. aspleniifolius Santa Cruz Island ironwood

Lyonothamnus floribundus subsp. aspleniifolius blooming in early summer on Bowdoin Street. Sairus Patel, 7 Jun 2018

Lyonothamnus floribundus subsp. aspleniifolius leaf. From Trees of Stanford and Environs, Ronald Bracewell

A charismatically attractive tree from the California Channel Islands, it grows with a narrow, upright habit. Distinctive, fern-like leaves are elegantly divided into 3–7 pinnately arranged leaflets, each of which is further dissected right to its midvein into scalloped segments – neither true teeth nor separately stalked leaflets. “Paracompound” is a catch-all designation for this kind of curious, intermediate architecture. Even the rachis, though not the leaf stalk itself, is winged with similar segments. The subspecies name evokes the fronds of Asplenium ferns. Some note a resemblance to the leaf of Cannabis, though the latter is palmately compound, its leaflets radiating from a single point, unlike the pinnate pattern seen here.

The bark is wonderfully handsome, peeling in long, flat strips to reveal a rich cinnamon-rust underlayer; older bark weathers to a soft gray. Substantial burls at the base of the trunks attest to the species’ tendency to form multiple stems; on its native islands, it often grows in clonal groves, some with more than a hundred trunks.

In late May, flat-topped clusters of creamy flowers are abundantly produced (floribundus); they are remarkably similar to those of the unrelated buckwheat (Eriogonum). As the season progresses, the fruits develop: pairs of brown woody follicles, ⅛ inch across, nestled within the persistent calyx. These remain on the flower heads, blackening or fading to gray, often lingering for years. Though this may not please every eye, the juxtaposition of fresh blooms with older clusters in various states of decay, all set against bright green foliage on reddish twigs, creates a tapestry that is striking and certainly unique.

Nearly a score of trees grow on the south side of Bowdoin Street between Pine Hill Road and Stanford Avenue; a couple are on the north side too. Others appear just around the corner in the Stanford Avenue greenbelt, beginning at the Santa Fe Avenue bike path and continuing past the Sonoma Terrace path, extending into the clearing about 75 yards beyond (map pin). A solitary specimen stands at the end of the parking lot between Branner Hall and Kimball Hall; another anchors the northwest corner of Encina Hall. A small grove once grew near the northeast side of Encina Hall, at the former Eating Clubs there, but these were removed to make way for McDonald Hall.

The tree is often misleadingly called Santa Catalina Island ironwood, or some variant thereof. That epithet should be reserved for the rare L. floribundus subsp. floribundus, which bears simple, undivided leaves and is found only on Santa Catalina Island. Subspecies aspleniifolius is restricted to Santa Cruz, San Clemente and Santa Rosa Islands. The genus honors naturalist William S. Lyon; thamnus is Greek for shrub. Fossil evidence indicates that now-extinct members of the genus were widespread in the western U.S. during the Neogene.

Illustrations: leaf.

Name derivation: See text above.