Which of these trees is not a conifer?

Populus is a genus of 25–35 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar, aspen, and cottonwood.

In the September 2006 issue of Science Magazine, the Joint Genome Institute announced that the western balsam poplar (P. trichocarpa) was the first tree whose full DNA code had been determined by DNA sequencing.

A pine is any conifer in the genus Pinus of the family Pinaceae. Pinus is the sole genus in the subfamily Pinoideae. The Plant List compiled by the Royal Botanic Gardens, Kew and Missouri Botanical Garden accepts 126 species names of pines as current, together with 35 unresolved species and many more synonyms.

A spruce is a tree of the genus Picea /paɪˈsiːə/, a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. Spruces are large trees, from about 20–60 m (about 60–200 ft) tall when mature, and have whorled branches and conical form.

Larches are conifers in the genus Larix, of the family Pinaceae (subfamily Laricoideae). Growing from 20 to 45 m (66 to 148 ft) tall, they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains further south. Larches are among the dominant plants in the boreal forests of Siberia and Canada.