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Helianthus annuus, sunflower. Note the conspicuous green
involucral bracts or phyllaries outside and below the peripheral ray flowers. On the right
are several intact disk flowers, each with a greenish corolla tube and 5 yellow lobes.
Parts of several florets have been removed to reveal the white, inferior ovaries, a few of
which still have one or both of the very pale pappus scales attached to their summits at
the flanks of the tiny annular nectary that encircles the scar where the style was
attached. The tip of a yellowish green receptacular bract can be seen at the outer or left
edge of each ovary in view. |
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Tridax procumbens, coat buttons. The heads on the left have a
series of green involucral bracts or phyllaries enclosing two kinds of florets. The
3-notched white corollas at the periphery belong to the zygomorphic female ray flowers.
The more numerous yellowish perfect, tubular, actinomorphic flowers in the center are
called disk flowers. Each of them has an associated receptacular bract or chaff scale that
is not readily visible unless the head is dissected or until it matures and sheds its
fruits as is the case with the head on the right. Two achenes (cypsellas) with highly
modified calyx (pappus) of pectinate bristles are also visible. |
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Gaillardia aristata, brown-eyed susan. Note the peripheral
involucral bracts and 3-notched ray florets, and central disk florets (upper photo). In
the lower photo, the fruits are shattering from the mature head. Each achene has a crown
of bristle-tipped scales that represents the modified calyx or pappus. Close attention to
the receptacle will reveal the bristly chaff or receptacular bracts that were associated
with the disk florets. |
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Lipochaeta remyi, nehe. This Hawaiian endemic has female ray
flowers and bisexual disk flowers. The upper heads are in an early fruiting stage and show
persistent, conspicuous yellowish green receptacular bracts in the center of the heads and
darker, purple-marked involucral bracts at the periphery. |
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Bidens amplectens, koko'olau. This Hawaiian endemic species is
another typical member of the Heliantheae tribe, although the receptacular bracts aren't
obvious in this photo. A common weed, Bidens pilosa, has some populations with discoid
heads and others with radiate heads. |
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Bidens pilosa, beggars tick. The highly modified calyx or pappus
as it is called in this family in this species takes the form of two or three barbed awns
at the tip of each ovary. These very effectively increase dispersal of the fruits by
mammals and birds. |
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Argyroxiphium sandwicense ssp macrocephalum, Haleakala
silversword. The well-known Hawaiian silversword evolved from members of Heliantheae that
are found on the west coast of North America. Adaptive
Radiation of the Hawaiian Silversword Alliance |
