Dr. Christenson is a research taxonomist with strong interests in the Aeridinae (Sarcanthinae), neotropical floristics, and the conservation of horticultural plants. He authored a monograph of Phalaenopsis for the International Phalaenopsis Alliance (IPA) in 2001. He has done field work in both Guyana and French Guiana and authored the orchid treatment for the Vascular Flora of Central French Guiana. He is also actively assisting David Bennett of Lima, Peru, with a modern inventory of Peruvian orchids. To date they have published 800 illustrations as Icones Orchidacearum Peruviarum, including more than 150 new distribution records and more than 100 new species from Peru. His bilingual florula Machu Picchu: Orchids was published in 2003. A prolific author of more than 300 publications, Dr. Christenson is known for his articles that attempt to bridge the gap between taxonomy and horticulture as well as his in-depth book reviews. He is a strong advocate for orchid conservation, particularly ex situ propagation, and actively works with commercial growers to that end.