Each leaf is narrow, 1-2 mm (less than 1/8in) wide, and broadens to a swollen base where it attaches in clusters to a bulb-like, underground rhizome, a characteristic of all quillwort species except mat-forming quillwort, I. tegetiformans. This swollen base also contains male and female sproangia protected by a thin, transparent covering (velum) which is used diagnotically to help identify quillwort species. Like mat-forming quillwort, black-spored quillwort also produces dark-colored female spores. Other Georgia quillworts have light-colored female spores.
The roots of black-spored and mat-forming quillworts are also useful in distinguishing between the two species. Roots arise from the underground rhisome in both species, but those of black-spored quillwort fork while those of mat-forming quillwort do not fork.
General Habitat: Only six counties in Georgia are known for this aquatic plant, none in the Savannah Basin. It occurs in Pickens County, South Carolina. This plant grows in small, wet granite depressions and can regenerate with rain after a dry spell. Its habitat, granite outcrops, is like that of mat-forming quillwort with which it could be easily confused. The difference in habit- spreading for mat-forming quillwort, and condensed clusters for black-spored quillwort- is probably the most useful way of initially distinguishing between these two related species.
General Description: Isoetes species are non-flowering plants allied to ferns. They are frequently mistaken for small, aquatic grasses but lack the hollow stems, nodes, and flat leaves of typical grasses. Quillwort leaves are hollow, quill-like, and reveal cross-like partitions when cut in cross section. The leaves of black-spored quillwort are stiff to arching and usually less than 8 cm (3in) tall, but generally longer than those of mat-forming quillwort (5 cm; also described in this manual). 