Macoun’s meadowfoam (Limnanthes macounii) COSEWIC assessment and status report: chapter 6

Biology

Macoun's meadowfoam is a winter annual. It germinates after the first heavy rains from late September to November (with some additional germination through the winter), blooms from late March to early May, and produces nutlets by the beginning of June.

Like many other annual species, Macoun's meadowfoam seeds have strong dormancy. In a rough experiment conducted by the writers about 50 seeds were planted; only three germinated the first year. It has been found in other species of the genus Limnanthes that seed germination is triggered by the drop in the air temperature (Toy & Willingham 1967); this could be the case in Macoun's meadowfoam as well.

Macoun's meadowfoam is among many annual species that germinate in the early fall after the first heavy rains. This early germination gives it a certain advantage, since it can produce most of its biomass in the time when it is not overgrown by other species. December and January is also the best time to look for the plant; its cotyledons are conspicuous and leaves are not overgrown with other vegetation.

Winter survival depends on the weather and the plant's location. In the severe winter of 1987/88, those plants that were submerged in water of vernal pools mostly died, whereas those that were above the waterline, partly survived. In an average winter, certain populations can be reduced to about 60% of the original number, others would come through without any losses. Winters warmer than average give a certain advantage to introduced perennial grasses that in turn results in the decrease of Macoun’s meadowfoam populations. In the relatively mild winter of 2002/2003, perennial grasses did not start to grow early; they may have suffered due to the droughts in a series of extremely dry summers over the last several years.

Macoun's meadowfoam flowers from the end of March to the beginning of May. The species is most probably self-pollinated or has autogamous flowers and it can produce fruit without any cross-pollination.

Up to four nutlets can be formed in each flower. Nutlets are relatively large and in fact they are largest from the cohort of all our native annuals. The plant is most probably barochoric, i.e., nutlets fall off and do not have any dispersal agents. In April, young nutlets are yellow-green and quite conspicuous.

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