▁flowers ▁called ▁ray ▁flowers , ▁and ▁the ▁" sun ▁disk " ▁is ▁made ▁of ▁smaller ▁circular ▁sh aped ▁individual ▁flowers ▁called ▁disc ▁flowers . ▁The ▁word ▁" aster " ▁means ▁" star " ▁in ▁Greek , ▁referring ▁to ▁the ▁appearance ▁of ▁some ▁family ▁members , ▁as ▁a ▁" star " ▁surrounded ▁by ▁" ray s ". ▁The ▁cluster ▁of ▁flowers ▁that ▁may ▁appear ▁to ▁be ▁a ▁single ▁flower , ▁is ▁called ▁a ▁head . ▁The ▁entire ▁head ▁may ▁move ▁tracking ▁the ▁sun , ▁like ▁a ▁" sm art " ▁solar ▁panel , ▁which ▁maxim izes ▁reflect ivity ▁of ▁the ▁whole ▁unit ▁and ▁can ▁thereby ▁attract ▁more ▁pol lin ators . ▁At ▁the ▁base ▁of ▁the ▁head , ▁and ▁surrounding ▁the ▁flowers ▁before ▁opening , ▁is ▁a ▁bundle ▁of ▁se pal - like ▁b ract s ▁or ▁scales ▁called ▁ph yll aries , ▁which ▁together ▁form ▁the ▁invol u cre ▁that ▁protect s ▁the ▁individual ▁flowers ▁in ▁the ▁head ▁before ▁opening . ▁The ▁individual ▁heads ▁have ▁the ▁smaller ▁individual ▁flowers ▁arranged ▁on ▁a ▁round ▁or ▁d ome - like ▁structure ▁called ▁the ▁re cept acle . ▁The ▁flowers ▁m ature ▁first ▁at ▁the ▁outside , ▁moving ▁toward ▁the ▁center , ▁with ▁the ▁young est ▁in ▁the ▁middle . ▁ ▁The ▁individual ▁flowers ▁in ▁a ▁head ▁have ▁ 5 ▁f used ▁pet als ▁( rare ly ▁ 4 ), ▁but ▁instead ▁of ▁sep als , ▁have ▁thread like , ▁hair y , ▁or ▁br ist ly ▁structures ▁called ▁p app us , ▁which ▁surr ound