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Lycopodiaceae

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Lycopodiaceae is a diverse family of ancient vascular plants. This group includes all core clubmosses and firmosses. There are about 17 accepted genera and roughly 500 known species. These plants are not spermatophytes, meaning they do not produce seeds. Instead, they rely on spores for reproduction. Many people call them "wolf foot" because their roots or branch tips resemble a wolf's paw.

These plants have a unique physical structure. Every member of the family possesses a microphyll. A microphyll is a small leaf with a single vein. These leaves do not have a leaf gap in the central vascular system. Often, these microphylls densely cover the stem in a scale-like or spiral pattern. Most clubmosses grow to a height of 5 to 20 cm. They produce spores on a specialized structure at the shoot's apex called a strobilus. A strobilus looks like a tiny battle club, which is where the name "clubmoss" comes from.

The life cycle of Lycopodiaceae involves complex biological stages. The plants are isosporous, meaning they produce spores that are all the same size. These spores are oily and highly flammable. The gametophytes, or the stage of the life cycle that produces gametes, are often non-photosynthetic. Many species are myco-heterotrophic, meaning they get nutrients from fungi. However, some members of the subfamily Lycopodielloideae have green, photosynthetic upper parts. These parts connect to colorless lower parts that touch fungal hyphae.

Taxonomists use molecular phylogenetic studies to group these plants. Under the PPG I system, the family is divided into three subfamilies. These are Lycopodielloideae, Lycopodioideae, and Huperzioideae. The Huperzioideae are distinct because they produce spores in small lateral structures within leaf axils. Some scientists suggest this group should be its own separate family. Most species in the family have a chromosome count of n=34. An exception is the genus Diphasiastrum, which has a count of n=23.

The evolutionary history of this family is incredibly long. Lycopodiaceae originated about 380 million years ago during the early Devonian. They split from the branch leading to Selaginella and Isoetes about 400 million years ago. The subfamilies Lycopodioideae and Huperzioideae diverged about 350 million years ago. This group has evolved very slowly over time. About 30% of their genes remain in syntenic blocks, which means they stay in the same arrangement. They have also undergone independent whole genome duplications.

Evidence shows the crown group of Lycopodiaceae emerged by the Triassic-Jurassic boundary. This was approximately 200 million years ago. A member of the Lycopodioideae crown group was found in China during the Early Cretaceous. These plants are cosmopolitan, meaning they are found worldwide. They are most common in tropical mountain and alpine environments. However, they are generally excluded from arid or dry environments. They can grow as terrestrial plants or as epiphytes.

Humans have found several practical uses for these plants throughout history. The genus Diphasiastrum is often used as greenery for Christmas decorations. Because the spores are oily and flammable, they have been used as a flash powder. Violin makers have used these spores for centuries to fill pores in wood. In Cornwall, people historically gathered club mosses during certain lunar phases. They used the plants as a remedy for eye disease.

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