midrib

noun3

1. •
   The strengthened vein down the middle of a flower petal or simple leaf or leaflet.

   • The midribs of the immense leaves form one of the most useful articles in these lands, supplying the place of bamboo, to which for many purposes they are superior. — 1869
2. •
   The continuation of the petiole of a pinnately compound leaf around which the leaflets attach.
3. •
   The shaft of a feather.