| Summary: | Archaic fems of the Ophioglossaceae family are rare in Europe. Recently a rapid decline of those ferns has been observed in many countries. Unfortunately, the demographic structure of Ophioglossaceae fern populations is poorly understood. Two groups of sporophyte developmental phases were distinguished in the study of Botrychium lunaria (L.) Sw. populations in Lithuania: active (elevated above the soil surface) and passive (subterranean) demographic groups. The active demographic group was divided into the following developmental phases; virgin (v), fertile (f1 , f2 and f3) and sub-senile (ss). The passive one was likewise divided into: sprouts (sp), juvenile (j) and secondary dormant sporophytes (sd). The main discriminating criteria of the developmental phases were: the relationship with the gametophyte, leaf differentiation into trophophore and sporophore, the degree of trophophore and sporophore development, and the degree of sporophore sporification. An additional criterion was the biological age of the sporophyte (determined by the counting of roots).
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