daviswj's Identifications

Of the various kinds of organisms that cause plant disease, plant-parasitic algae are not the norm: the only species common in the USA is this one, a plant pathogen infecting tea, coffee, and coconut plants, causing algal or rust algal leaf spot (a.k.a green scurf) on over 200 plant species (more than 60 families) from NC to FL and into TX, most commonly plants with somewhat leathery leaves, like this magnolia, or camellia & holly

Older algal colonies that become colonized (lichenized) by a fungus turn into leaf spot lichens, composite organisms of an alga and a fungus, then classified in the genus Strigula, the only lichen parasitic on plants, most visible on leaves, but also twigs & branches, even fruit, the crusty gray-green to greenish-brown color circular/blotchy spots generally somewhat raised from the plant surface, the edges often wavy or feathered; however, in summer, when the alga reproduces, the spots turn a velvety red-brown due to the production of reddish, spore-producing structures... numerous colonies can cause premature yellowing and loss of leaves