Retrorse. Directed back or downward.
Retuse. With a shallow notch at a rounded apex.
Revolute. Rolled backward from the margins or apex.
Rhachis. The axis of a spike or of a compound leaf.
Rhaphe. The ridge or adnate funicle which in an anatropous ovule connects the two ends.
Rhizome. Any prostrate or subterranean stem, usually rooting at the nodes and becoming erect at the apex. Very variable in character, and including morphologically the tuber, corm, bulb, etc.
Rhombic, Rhomboidal, Somewhat lozenge-shaped; obliquely four-sided.
Rib. A primary or prominent vein of a leaf.
Ringent. Gaping, as the mouth of an open bilabiate corolla.
Root. The underground part of a plant which supplies it with nourishment.