The arrowhead piculet is long and weighs . Adult males have a black cap with a red patch on the forehead and white spots on the rest of it. Their face is mostly dark brown with white tips on some feathers and a white line behind the eye. Their upperparts are olive brown whose feathers have blackish wedge-shaped centers, a very thin black bar at their tip, and a white spot just inside the tip. Their rump is plainer but their undertail coverts can have dark bars. Their flight feathers are brown with light buffy edges, especially on the secondaries and tertials. Their tail is brownish black; the innermost pair of feathers have mostly white inner webs and the outer two pairs have a white stripe on the outer webs. Their chin, throat, and sides of the neck are whitish with blackish bars. Their underparts are white with a brownish buff tinge on the belly and flanks; the underparts' feathers have brownish black fringes that give a scaly appearance. Adult females are identical but for no red on the forehead. Juveniles have a plain brown crown; their upperparts are browner than the adults' and have blackish bars. Their underparts are duller with a more obscure pattern.Winkler, H., D. A. Christie, C. J. Sharpe, and A. Motis (2020). Arrowhead Piculet (Picumnus minutissimus), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.arrpic1.01 retrieved January 11, 2023
