His early interest in mycology gave rise to his 1953 publication, with others, of “Enumeratio Uredinearum Scandinavicarum”, a catalogue of rust fungi, but Hylander's greatest contribution was within Swedish vascular plant taxonomy, where he appears as one of the major figures of the twentieth century.
The Flora work entailed his own basic research, which involved a critical examination of herbarium material and literature and some experimental crops and field studies.
Hylander's treatment of the Nordic vascular plants takes a modern approach and is characterized by deep insights concerning, for example, species variation in the field.
These editions contained several significant novelties for Nordic floristics both in terms of nomenclature and systematics, as more fully discussed in an important work “Nomenklatorische und systematische Studien über nordische Gefässpflanzen” (1945).
Hylander's great insights into Nordic vascular plant taxonomy led to several international assignments, including as a regional adviser for Flora Europaea.
Hylander showed his taste for taxonomically difficult plant groups in a couple of studies of the genera Alchemilla and Mentha.
Hylander reported occurrences of such in a variety of small essays, and as a final product of this work, one can consider the posthumously published “Prima loca plantarum vascularium Sueciae”, whose manuscript was completed a few months before his death.
His special interests are reflected in the garden's finest attractions and in both scientifically and aesthetically well-designed species selection.