Fischeriana A (1), a new meroterpenoid with a rare carbon skeleton, along with one of its known biosynthesis-related compounds 2,4-dihydroxy-6-methoxyacetophenone (2) and two known ent-abietane-type diterpenoids (3-4), were isolated from the roots of Euphorbia fischeriana. Their structures, including the stereochemistry, were elucidated using comprehensive spectroscopic methods, single-crystal X-ray diffraction, and electronic circular dichroism analysis. Compound 1 was found to be made up of an unusual heptacyclic ring system (6/6/5/5/5/6/6) featuring a modified ent-abietane diterpene with a phloroglucinol moiety. A possible biogenetic pathway for 1 was proposed. Compound 1 exhibited marked anti-tumor activities against the HepG2 cell line.