sphenopsid
Quick Summary
The lone tree with horizontal grooves in the right foreground is a jointed sphenopsid (Calamites); the large trees with scar patterns are lycopsids.
The term "sphenopsid" refers to a class or division of primitive, spore-bearing vascular plants known as Equisetopsida. These plants are characterized by jointed, ribbed stems and leaves that are typically arranged in whorls at distinct nodes along the stem. Reproductive structures, called cones or strobili, form at the ends of branches.
Most sphenopsids are extinct, with fossil evidence dating back to the Devonian Period. The only living genus is Equisetum, which includes about 15 species commonly known as horsetails and scouring rushes. These plants are found worldwide, except for Australia, New Zealand, and Antarctica. While the extinct forms included large trees, modern Equisetum species are generally herbaceous and less than a meter tall, though some tropical species can reach up to 10 meters. Historically, the silica-rich cell walls of horsetails made them useful as scouring agents.123
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