Picea mariana 'Horstmann's Dwarf' is a narrow, irregular-upright dwarf selection of black spruce with extremely variable, at times clumpy branching and species-typical fine, Blue-green needles with prominent foliar buds, particularly in winter. After 10 years of growth, a mature specimen will measure 24 - 30 inches (30 - 45 cm) tall and half as wide, an annual growth rate of 2 to 2.5 inches (3 - 4.5 cm).
This cultivar although very interesting is of unknown origin. It's cultivar name suggests that it was introduced at some point by Horstmann nurseries, Schneverdingen, Germany.