For 40 years he taught courses in general biology, general botany, plants & people, and plant identification. He is also author of the popular natural history website called Wayne's Word: An Online Textbook Of Natural History, including 4 decades of lecture material placed on blackboards & whiteboards during his teaching career. He has studied & photographed duckweeds extensively in California (subfamily Lemnoideae), including the world's smallest flowering plants, and wrote the duckweed section for The Jepson Manual: Vascular Plants of California (2nd Edition). His articles and photo images have appeared in more than 240 natural history publications.
Armstrong's special areas of interest include the taxonomy of duckweeds, lichen symbiosis, the fig & its symbiotic wasp, drift seeds & fruits that float across oceans, botanical jewelry & the coconut pearl hoax, poison oak immune response, amazing plants (botanical record-breakers), California floristics (including Brodiaeas in California), and the evolution & adaptations of organisms. He wrote a Master's Thesis on Cupressus. Although primarily a botanist, he has once again focused his attention on ant diversity, his childhood passion. He is a Professor Emeritus in the Life Sciences Department at Palomar College, San Marcos, California.