Philipp Wilhelm Wirtgen (December 4, 1806 - September 7, 1870) was a German botanist and teacher who was a native of Neuwied.
He was a school teacher in Remagen, Winningen and beginning in 1831 at Koblenz. With botanist Theodor Friedrich Ludwig Nees von Esenbeck (1787-1837), he was founder of the Botanischer Verein am Mittel- und Niederrhein (Botanical Association of the Middle and Lower Rhine).
Wirtgen specialized in the study of Rhineland flora, and his work largely dealt with phytogeography, taxonomy and floristics in the field of botany. Among his numerous publications was an 1857 book involving flora from Rhine Province called Flora der preußischen Rheinprovinz und der zunächst angränzenden Gegenden, and a treatise titled Neuwied und seine Umgebung (Neuwied and its Environment).
The plant genus Wirtgenia from the family Poaceae is named after him.