Zara picks a sunflower and says it is one big flower…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Zara picks a sunflower and says it is one big flower. Her teacher says that the head is a cluster. (a) What is the correct name of the head? (b) Is its arrangement racemose or cymose? Give a reason. (c) The ray florets are epigynous. What does that say about their ovary? (d) Name the placentation seen in sunflower.
Need a reminder? The key ideaShow
An inflorescence is the arrangement of flowers on the floral axis. Racemose: the main axis continues to grow, flowers open in acropetal order, the oldest at the base and the youngest at the tip. Cymose: the main axis ends in a flower, growth is limited, flowers open in basipetal order. The pedicel is the stalk of one flower; the peduncle is the stalk of the cluster. A flower has the calyx, corolla, androecium and gynoecium. Bisexual or unisexual; actinomorphic, zygomorphic or asymmetric. Hypogynous (superior ovary), perigynous (half inferior), epigynous (inferior). Aestivation: valvate, twisted, imbricate, vexillary. Stamens: filament and bilobed anther with four pollen sacs; epipetalous, epiphyllous, monoadelphous, diadelphous, polyadelphous. Carpel: ovary, style, stigma; apocarpous or syncarpous. Placentation: marginal, axile, parietal, free central, basal.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The name. The head is an inflorescence, made of many small flowers called florets.
Step 2. The type. It is racemose, because the main axis keeps growing and does not end in one flower.
Step 3. The ray florets. In an epigynous flower the thalamus grows around the ovary and fuses with it. The other parts arise above it, so the ovary is inferior.
Step 4. Placentation. Sunflower has basal placentation: a single ovule on a placenta at the base of the ovary.
Answer: (a) an inflorescence of florets; (b) racemose; (c) the ovary is inferior; (d) basal.
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