Cycas revoluta, commonly known as the sago palm, king sago palm, or sago cycad, is an ancient woody plant belonging to the family Cycadaceae. Despite its common name and palm-like appearance, it is not a true palm at all, but rather a gymnosperm more closely related to conifers and ginkgos. Native to southern Japan, particularly the Ryukyu Islands, Cycas revoluta is a living fossil whose lineage dates back hundreds of millions of years to the Mesozoic era. The genus name Cycas is derived from the Greek word koikas, meaning a kind of palm, while the species epithet revoluta is Latin for "rolled back," describing the distinctive downward-curling margins of the plant's leaflets.

The plant features a thick, stout, woody trunk that is typically covered in the persistent, rough remnants of old leaf bases. Growing very slowly, mature specimens often reach heights of 1 to 2 meters, occasionally taller over decades. At the top of the trunk sits a stiff, symmetrical, and ornate crown of dark green, glossy, pinnate leaves (fronds) that can grow up to a meter or more in length. Each frond consists of numerous rigid, narrow leaflets with sharply pointed tips and downward-rolled edges. As gymnosperms, cycads are dioecious, meaning individual plants bear either male or female reproductive structures rather than flowers. Mature female plants produce a large, golden, woolly central megasporophyll cone resembling a giant pinecone or blooming globe, which carries bright red-orange seeds, while male plants produce a prominent upright cylindrical pollen cone.

In traditional and historical contexts, particularly during times of famine in the Ryukyu Islands, Cycas revoluta served as an emergency source of starch, often referred to as "sago." However, unlike true sago palms (Metroxylon), every part of the cycad plant—especially the seeds and pith—is heavily laced with potent neurotoxins and carcinogenic compounds, requiring extremely meticulous, multi-step washing, leaching, and fermentation processes to render it edible. Because of this extreme toxicity, the plant is rarely utilized for direct food production today outside of specialized traditional preparation methods. Instead, it has achieved global popularity as a prized ornamental plant in subtropical and tropical landscaping, as well as a favorite subject for indoor container gardening and bonsai culture due to its architectural symmetry and hardiness.

From a toxicological and biochemical perspective, Cycas revoluta is notorious for containing dangerous secondary metabolites that protect it from herbivores. The primary toxins are cycasin (a toxic glycoside that breaks down into carcinogenic methylazoxymethanol) and b-methylamino-L-alanine (BMAA), a neurotoxic amino acid linked to neurodegenerative disorders. Ingestion of any part of the plant by domestic animals—such as dogs and cats—or humans leads to severe liver failure, vomiting, neurological damage, and high mortality rates, making pet safety a major concern when cultivating the plant.