Serotinous Plants of Schofield Rd Bushland

Main Club Excursion June 2020

With COVID-19 restrictions easing, the club is organising excursions once more. To celebrate, a group of 20 members and guests met for a guided walk through the bushland at the end of Schofield Rd, Wattle Grove (Bush Forever site #50). We were led by Professor Byron Lamont and Dr Phillip Groom who together have been studying the plants in the reserve and literally wrote the book on Plant life of Southwestern Australia. They know the plants so well that by the time we arrived they had already scouted the reserve and helpfully labelled many specimens of plants!

Allocasuarina humilis
Dwarf Sheoak (Allocasuarina humilis), pre-labelled by Byron and Phillip. The red drawing pins highlight successive years of fruits still held on the plant, the most recent at top left.

The focus of the excursion was serotinous plants – species which store their seeds on the plant rather than releasing them onto the soil – a subject on which Byron is an international authority and has previously spoken to the club about. After splitting into two smaller groups, our guides provided some background about serotiny, including that 75% of the world’s serotinous species grow in South West WA. They also described the variation that occurs and what that tells us about their ecology. For example, Banksia attenuata retains its spent flowers on the cone that holds their seeds. This makes them more flammable, a benefit as the heat from a fire melts the resin that holds the follicles closed, thus allowing them to then open and release their seed onto the ash bed. Banksia menziesii cones will open more readily in the heat of summer, making it less reliant on fire, so it does not retain its old flowers.

Eremaea pauciflora was shown as an example of a plant that can survive fires by resprouting from a lignotuber, so it has less need to flower profusely and set lots of seed than species that are killed by fire. Byron noted that many eucalypts are an exception to this rule, both setting lots of seed AND being able to resprout after fire.

On-plant storage protects seeds from fire but leaves them vulnerable to seed-eating birds and insect larvae, so many of the plants we were shown hide their seed capsules behind spiky leaves, as some of us experienced when brushing past the Hakea ruscifolia.

Hakea ruscifolia
Candle hakea (Hakea ruscifolia) with brown woody fruits hidden amongst the spiny foliage. Photo: S. Lofthouse

Another evolved tactic is fruits that resemble the leaves. One of the most magnificent examples of this is the Hakea trifurcata. Most of the leaves on this plant are thin and needle-like but once they are mature and start producing seeds, the plant also produce wide leaves which curl into a shape that resembles a large fruit capsule. As part of his PhD, Phillip fed branches of this plant to captive cockatoos and found that they became confused and gave up after picking off a few of these false seed pods.

Hakea trifurcata
Two-leaf hakea, Hakea trifurcata. The fruit containing the seeds (at tip of index finger) is hard to spot amongst the large curled leaves. Photo: S. Lofthouse

We are very grateful to Byron and Phillip for not only guiding and identifying the plants for us, but for describing the fascinating relationships they have with fire, animals and the local ecosystem.

Steven Lofthouse