Lewis & Short

myrtus (murtus), i and ūs, f., = μύρτος, a myrtle, myrtle-tree, Plin. 15, 29, 37, § 122: viridi caput impedire myrto, Hor. C. 1, 4, 9.
Poet., for a spear of myrtle-wood: et pastoralem praefixā cuspide myrtum, Verg. A. 7, 817.
Nom. plur. myrtūs, Verg. G. 2, 64.
As masc., Cato, R. R. 8.
Anteclass. also, myrta or murta, ae, f.: murta nigra, Cato, R. R. 125.
Murtus for myrtus: murti nigrae baccae, Scrib. Comp. 109.