Atelocauda digitata, at present considered indigenous to Hawai‘i, also occurs on a number of Acacia hosts in Australia, New Zealand, and Java.  The rust, earlier described as Uromyces phyllodiorum, a demicyclic species in Australia, but has been shown to be macrocyclic in Hawai‘i (Hodges and Gardner, 1984, 1994a).  The spermogonial and aecial states occur on witches'-brooms that consist of broad, fleshy, much thickened phyllodes.  A comparative study of these forms is currently underway.

Spermogonial-aecial witches'-brooms of A. digitata.

Although infection with A. digitata is most commonly systemic, resulting in production of witches'-brooms, spermogonial-aecial infections are also occasionally observed on individual phyllodes.  Infection sites are usually conspicuous, and comprised of hypertrophied tissue which is concave on one surface and convex on the other.

A tree of Acacia koa with numerous witches'-brooms of A. digitata.

Flowering shoots infected with A. digitata.

  Closeup of spermogonia (large arrow) and aecia (small arrow) of A. digitata.  In the original description of A. digitata (as Uromyces koae) (Stevens, 1925) the aecia were described as uredinia based on the morphological resemblance of the sproes to urediniospores.  More recently, this spore state has been recognized as the aecial due to its association with spermogonia (Gardner et al., 1979), and the true urediniospores have been discovered (see below).

    Uredinia and telia of A. digitata.

A. digitata aeciospores showing reticulate surface pattern characteristic of Atelocauda and prominent equatorial germ pores.

  The germ tube of a germinating aeciospore on a leaf surface entering a stomate (arrow).

    Teliospores of A. digitata showing variation in morphology and apical ornamentation.

  Median view through the subapical germ pore (arrow) of a teliospore of A. digitata.

     Urediniospores of A. digitata with wall markings and germ pores resembling those of aeciospores, but with a pedicel and an apical thickening.  Aeciospores from certain locations have a similar, slightly thickened apex, however.

   Mixture of urediniospores and teliospores of A. digitata, where these spore states occasionally are found together in the same sorus.  More frequently, they occur in separate sori.