Hope’s Cycad – Lepidozamia hopeii

Growing at an estimated meter per century, the venerable Hope’s Cycad – Lepidozamia hopei (W.Hill) Regel, attains a potential height of twenty-metres across two-millennia.  Reproducing about once every seven years, with both male and female plants producing large reproductive cones atop their axes, appears to be both periodic but also triggered by cyclones.  In the critical phase of cone development, when the female requires pollen produced in the male cone, delivered into the female, she calls out pheromonally.  The male plant responds to this chemical call-to-action at around eleven o’clock in the morning, by increasing the internal temperature within his cone by up to seventeen degrees Celsius.  The cone’s internal temperature becomes unbearably hot, driving the mass evacuation of resident weevils that feed and breed within the tissues of the male cone.  Escaping the heat, these primitive, pollen-encrusted insects, descend from the male cone along the outer-trunk, across the forest floor, up the trunk of the female cycad and ultimately into the source of the chemical signal, thus delivering pollen.  There they remain, until about three o’clock in the afternoon, when the female plant increases the internal temperature of her cone by up to seventeen degrees Celsius, sending the insects back from whence they came and for two to three weeks, this play on temperature and the chemical communications between the male and female cycads, ensures the reliable delivery of pollen by flightless insects.

The retention of this primitive reproductive process speaks volumes about the extraordinary evolutionary history of one of the world’s first producers of seeds.  Having obviously developed the process before insects evolved the capacity for flight, the same strategy is retained to the present time, in a landscape that has long been enriched with flying insects that could otherwise make the delivery of pollen much more efficient.  However, the plant species has not aspired to change, since the existing system is working perfectly well.