Mystery Tree: Grevillea robusta

Photo: Rick J. Pelleg, 2005.

The tree we saw during our Wild Woodlands programs on April 25 and 26 is a silky oak (Grevillea robusta), sometimes also referred to as a silver oak. It is native to Australia and is a member of the protea family. It is not in the oak family but got its common name from the oak-like grain of its wood.

Height: 15 – 40 m

Leaves: 10 – 30 cm long; 9 – 15 cm wide; bi- or tri-pinnately compound, making it fern-like in appearance; alternate on the stem; dark green with grayish-white or rusty undersides; leaves tend to be variable within the species.

Flowers: large, showy, gold to orange-yellow flowers; held in pairs on racemes (a type of stem) 7.5 to 10 cm long; each individual flower is slender and about 2.5 cm long; bottlebrush-like shaped; require summer heat to flower so those planted in San Francisco often do not flower.

Fruit/Seeds: a pod-like follicle, 20 mm in diameter, is slightly flattened and has a long-curved style; hard, dark-brown to black follicle splits open in late fall releasing the one or two seeds it contains; seeds are about 10 mm long, flattened, and surrounded by a membranous wing.

Further information:

• http://plants.usda.gov/java/profile?symbol=GRRO
• http://hort.ufl.edu/trees/GREROBA.pdf
• McClintock, Elizabeth. The Trees of Golden Gate Park and San Francisco. Berkeley, CA: Heyday Books, 2001.
• Olde, Peter & Marriott, Neil. The Grevillea Book. Vol. 3. Portland, OR: Timber Press, 1995.
• Rodd, Tony & Stackhouse, Jennifer. Trees: A Visual Guide. Berkeley: University of California Press, 2008.