Cyanea mceldowneyi is a shrub species that grows 2–3 meters tall, with unbranched stems ranging from muricate to aculeate. It exhibits dimorphic leaves: juvenile leaves are broadly elliptic to obovate, measuring 15–22 cm in length and 5–9 cm in width, while adult leaves are oblanceolate to narrowly oblong, spanning 20–35 cm long and 5–9 cm wide. Juvenile and adult leaves have acuminate apices but differ at the base—juveniles are rounded, whereas adults are cuneate. Juvenile leaves feature aculeate and pubescent upper surfaces with a pale green, pubescent, and aculeate lower surface. Adult leaves are green and glabrous or sparsely muricate above, with a very sparsely pubescent pale green underside. The axillary inflorescence comprises 5–7 flowers with peduncles 15–30 mm long and pedicels 10–14 mm long. The hypanthium is obconical, approximately 5 mm long and 4 mm wide. The calyx has oblong lobes, about 5 mm in length and 2.5 mm in width, with emarginate and apiculate apexes. The flowers feature a zygomorphic (bilaterally symmetric) white corolla with purple longitudinal stripes, roughly 40 mm long and 8 mm wide, arcuate tube, and muricate lobes about a quarter of the tube’s length. It possesses five stamens that are connate with glabrous anthers, the lower two having white hair tufts at their apices. The two-celled ovary is inferior, with axile placentation and a two-lobed stigma that becomes receptive after the pollen is expelled through the anther tube. It occurs in wet forests on the windward slopes, found at 925-1,280 meters.