← Glossary Morphology rachis The main axis of a compound leaf or fern frond, from which the leaflets or pinnae arise. An extension of the petiole . Plants Using This Term (1) Toxicodendron vernix — Poison Sumac Related Terms achene acuminate alternate annual axillary basal berry biennial bract calyx capsule cauline clasping cordate corolla crenate cyme cypsela deciduous dentate drupe entire evergreen glaucous inflorescence lanceolate ligulate lobed opposite ovary palmate panicle pappus pedicel perennial petiole pinnate pubescent raceme rhizome rosette sepal serrate sessile silique spadix spathe spatulate stamen succulent taproot ternate thallus trifoliate umbel undulate whorled