A mature koa forest.
An old, gnarled koa tree in Hawai‘i
Volcanoes National Park.Rusts on Acacia koa (koa) (Fabaceae)
Koa is the second most abundant overstory species in upper elevation forests, forming nearly pure stands in montane forests such as those on the slopes of Mauna Loa between approximately 4,000 and 7,000 feet (1,230 and 2,150 meters). Koa is distinctive in the formation of crescent-shaped phyllodes which in older trees assume the function of the pinnately compound true leaves produced in juvenile stages of development. As an endemic tree, koa is of critical ecological importance, forming habitat for numerous native birds, insects, and other flora and fauna. As a nitrogen-fixing leguminous species, koa is thought to account significantly for the nitrogen content of otherwise nitrogen-poor volcanic forest soils. Koa is also prominently represented in early Hawaiian legend and culture, and economically is considered the most valuable of the common native timber species. Koa wood, sometimes referred to as "Hawaiian mahogany," can be highly polished to emphasize its deep reddish coloration with wavy grain and is in high demand for furniture making, paneling, and such woodworking crafts as bowls and ukuleles.
A mature koa forest.
An old, gnarled koa tree in Hawai‘i
Volcanoes National Park.
The genus Atelocauda was relatively recently resurrected by Cummins and Hiratsuka (1983) to accommodate rusts of Acacia in Hawai‘i, Australia, and the Pacific formerly included in Uromyces. Atelocauda incrustans was retained as the type species, although there is reason to question the affinity of this species to the other members of Atelocauda. The type is not from the Pacific nor from an Acacia host, but was collected on Lonchocarpus sp. in Panama. Unfortunately, this rust is not known to have been found since the type specimen was collected. The species is microcyclic and thus lacks urediniospores or aeciospores, whose surface markings would otherwise furnish an indication of affinity. Other than the type species, all members of Atelocauda and Endoraecium have in common deeply sculpted reticulately (netted) ornamented aeciospores, or aecioid teliospores in the case of Endoraecium, a distinctive feature of these species but an unusual characteristic among the rust fungi in general. Prominent equatorial germ pores are also characteristic. Spore surface ornamentation of most rust fungi is of an echinulate (spikes or spines) or verrucose (bumps) type, or combination of these features. The genera Atelocauda and Endoraecium may be closer in affinity to the genus Uromycladium, which occurs on a number of Acacia and Albizzia hosts principally in Australia and New Zealand, (Cummins and Hiratsuka, 1983; Gardner, 1994a; Gardner and Hodges, 1985).
Endoraecium acaciae and E. hawaiiense