Long segments and identification
Leptocereus rosei produces segments up to 5 m long but only 10–15 mm in diameter. Surrounding vegetation supports the stems, which hang down when unsupported. A glossy green surface and 4 ribs, occasionally 5, with straight or slightly dentate margins distinguish it from the strongly undulate-ribbed L. velozianus. Areoles occur every 15–20 mm and bear 10–12 spines measuring 12–15 mm. There may be 2 shorter parallel spines at the base. [Hoxey et al. 2023b, pp. 51, 57]
The documented site
The revision authors knew the species from one site about 15 km west of Azua in the Dominican Republic. It grows in seasonally dry woodland on a non-rocky substrate of sand and clay. Plants observed near Las Guanábanas were at about 250 m elevation. In this revision, Rose’s historical collections from Azua, made in 1913, were assigned to L. rosei. Searches no longer confirmed plants at the former sites near the expanding town. [Hoxey et al. 2023b, pp. 51, 57]
Fruit and seeds
The stem tip may develop a short felted flowering region that later becomes woody. The fruit is elongated, about 55 × 30 mm, bright green and densely armed with spines. Approximately 20 spines, each 10 mm long, in an areole may overlap neighbouring clusters. Seeds measure about 3.4 × 2.0–2.2 × 1.4 mm. The revision authors did not present their own measurements of fresh flowers of this species. Their floral account uses the historical description and remnants retained on fruits. [Hoxey et al. 2023b, pp. 51, 57]