Asteraceae - Tribe Lactuceae
Asteridae: Asterales. The Lactuceae are a tribe of closely related
genera of the sunflower family that are easily recognized because the flowering heads are
composed of wholly of ligulate florets that are usually 5-lobed. Another very
distinguishing feature is the milky sap. Although not apparent without magnification, the
pollen is distinctive in that the spines are more or less restricted to discrete ridges or
flanges on the surface of the grain. In other members of the family the spines are
distributed more or less evenly over the surface of the pollen grain. The pappus usually
consists of scales or stiff hairs.
Each "thumbnail" image below is linked to a larger photograph.
 |
Chicorium intybus, chicory. Note the presence of only ligulate
florets in the head. The corollas are 5-lobed. Dark purple anther columns, white pollen
and the bifid style tips are also visible. |
 |
Youngia japonica, oriental hawksbeard. Notice the 5-lobed
ligulate corollas on all the florets in the head. |
|
Sonchus sp., sow thistle. This photo shows a side view of a head
of all ligulate florets and the subtending involucral bracts or phyllaries. White sap
which characterizes this tribe can be seen oozing from a cut stem. Some Lactuceae such as
this one have a beaked achene that bears persistent bristle like pappus segments that act
like a parachute to disperse the fruits (right photo). |
|
Taraxacum officinale, dandelion. This common lawn weed has the
pappus very effectively modified for wind dispersal of the fruit. Note the lack of chaff
or receptacular bracts on the receptacle. |
Flowering Plant Family Access Page
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