The Collaborative International Dictionary of English v.0.48:

Tickseed \Tick"seed`\, n. [Tick the insect + seed; cf. G.
   wanzensamen, literally, bug seed.]
   1. A seed or fruit resembling in shape an insect, as that of
      certain plants.
      [1913 Webster]

   2. (Bot.)
      (a) Same as Coreopsis.
      (b) Any plant of the genus Corispermum, plants of the
          Goosefoot family.
          [1913 Webster]

WordNet (r) 3.0 (2006):

tickseed
    n 1: any of numerous plants of the genus Coreopsis having a
         profusion of showy usually yellow daisylike flowers over
         long periods; North and South America [syn: coreopsis,
         tickseed, tickweed, tick-weed]