Groom & Lamont: Fruit and seed development in Hakea 
N 
P 
K 
Figure 3. Total nutrient content of N, P and K in the fruit (open symbol) and seed (filled symbol) of H. erinacea (top row) and H. 
trifurcata (bottom row). Ca and Mg show similar trends as K. For P, fruit and seed data are on separate axes. Arrowed-line represents 
period during fruit development when fruit were fleshy and non-woody. Data calculated from the average fruit dry mass and the dry 
mass of one seed. 
matured (after Hocking 1982) showed that N and P were 
redistributed with the greatest efficiency (80% and 48% 
respectively) and K, Ca and Mg with much less efficiency 
(0.5-19%). A decrease in total fruit nutrient content was 
associated with the onset of wood formation in the fruit 
walls of H. erinacea (Fig. 3). 
The total nutrient content (in mg) in the fruit of H. 
trifurcata reached a maximum 110 days after anthesis 
(Fig. 3) and was synchronised with the beginning of fruit 
wood formation. The total fruit nutrient content (in mg) 
for H. trifurcata reached its maximum (N: 3.17; P: 0.025; 
Ca: 0.56; Mg: 0.24) 115 days after anthesis (Fig. 3). 
Potassium peaked at 0.14 mg 150 days after anthesis. At 
the commencement of fruit wood formation the total 
nutrient content of one H. trifurcata seed was less than 
(N, P, Mg) or greater than (K, Ca) the amount present in 
a fully developed seed (Fig. 3). Redistribution efficiency 
of nutrients translocated from maturing follicles to seeds 
in H. trifurcata was low for K and Ca (10-15%), moderate 
for N and Mg (24-32%) and high for P (63%). 
Discussion 
Hakea erinacea and H. trifurcata have similar fruit and 
seed size, and produce mature fruits and seeds within 
similar developmental time-frames. The fruits of both 
species reached their maximum fresh mass during their 
'green', non-woody state, occurring with the 
commencement of wood formation in their fruit walls. 
Developing fruits are an important store of essential 
nutrients (e.g., N, P) (cf Hocking 1981, 1982) that were 
translocated to the two winged seeds at the onset of fruit 
wood formation. Within the Proteaceae, woody fruit 
protect the seeds from external damage by heat, 
desiccation and granivores, as well as providing an 
economical method of redistributing certain nutrients to 
the developing seeds (Stock et al. 1991, Lamont & Groom 
1998). 
The timing of fruit wood formation in Hakea follicles 
may be related to fruit size, which in turn is a function of 
the ability of the species to store seeds within their canopy 
(serotiny). Weakly serotinous Hakea species typically 
possess smaller, thinner walled follicles with less dense 
wood than more serotinous species (Groom & Lamont 
1997). By allocating a relatively small amount of carbon 
(130-180 mg dry weight) into their thin woody fruit walls, 
the weakly serotinous H. erinacea and H. trifurcata provide 
limited seed protection over a relatively short period of 
time, without affecting the efficiency with which certain 
nutrients are redistributed to the developing seeds. For 
fire-prone plant species, weak serotiny has evolved 
because costs (carbon invested in protection) outweigh the 
benefits (maximising recruitment) (Midgley 2000). 
Differences between maturation time and degree of 
serotiny is supported by Hocking (1982) who showed that 
the non-serotinous, leathery follicles of Grevillea wilsonii 
matured within 9 weeks of anthesis, compared with the 25 
weeks of the serotinous, woody fruit of the co-occurring 
Hakea undulata. 
137 
