New York Natural Heritage Program
Common Moonwort
Botrychium lunaria (L.) Sw.

General Description [-]
Moonwort is a very small, perennial fern with a single aboveground frond. The dark-green frond is usually about 4 inches long and can be seen through mid-summer. It is divided into two leaves above a common stalk. The sterile leaf is usually dark green, thick, and fleshy. It has up to nine usually overlapping pairs of broadly fan-shaped leaflets (pinnae). The top edges are rounded and smooth or wavy or rarely have teeth. The fertile leaf is longer than the sterile leaf with branches that bear grape-like sporangia. Spores germinate underground and develop into tiny, non-photosynthetic gametophytes which depend on a fungus for nourishment.

Best Life Stage for Proper Identification [-]
This fern is best identified when the leaves are fully formed.

Similar Species [-]
Botrychium lunaria is most easily confused with Botrychium minganense, Botrychium campestre, and Botrychium simplex. The pinnae of Botrychium minganense and Botrychium campestre are narrower, wedge shaped and do not overlap. Botrychium campestre has a shorter and more branched fertile leaf and the pinnae of the sterile leaf are often deeply divided at the top. It's leaves can only be seen in the spring. In Botrychium simplex the upper pinnules are somewhat fused together and not separate. The fertile leaf often arises from near the ground level. Botrychium matricariifolium pinnules are long and narrow with a central midrib and secondary segments. Reliable field determination of moonworts depends on the careful use of technical keys and comparison with silhouette outlines of verified specimens. Identification can be complicated because there is often a high degree of morphological variability between individuals in a population and between populations of the same species. Several species may grow together at the same site, and the few diagnostic characters may not be apparent in small plants.
Common Moonwort Images
click to enlarge
The Best Time to See
Mature fronds of this plant are visible from June to August. This should be the time of year when surveys for this species are conducted.
J F M A M J J A S O N D
Vegetative Fruiting
The time of year you would expect to find Common Moonwort vegetative (blue shading) and fruiting (orange shading) in New York.