Jacksonia macrocalyx

Jacksonia macrocalyx is an erect shrub that typically grows to 0.3–1.0 m (1 ft 0 in – 3 ft 3 in) high and 0.7–1.5 m (2 ft 4 in – 4 ft 11 in) wide. Its branches are greyish-geen, with sharply-pointed phylloclades 1.5–20 mm (0.059–0.787 in) long and 0.3–0.9 mm (0.012–0.035 in) wide. Its leaves are reduced to mid-brown, broadly egg-shaped scales, 0.5–2.5 mm (0.020–0.098 in) long and 0.5–1.2 mm (0.020–0.047 in) wide. The flowers are scattered near the ends of branches on a pedicel 2.5–4.0 mm (0.098–0.157 in) long, with narrowly lance-shaped bracteoles 1.5–1.8 mm (0.059–0.071 in) long on the upper part of the pedicels. The floral tube is 1.3–1.5 mm (0.051–0.059 in) long and the sepals are papery, with lobes 9.0–11.3 mm (0.35–0.44 in) long and 2.7–4.0 mm (0.11–0.16 in) wide. The flowers are yellow, the standard petal 8.7–10.3 mm (0.34–0.41 in) long and 12.6–17 mm (0.50–0.67 in) broad, the wings 11–14.1 mm (0.43–0.56 in) long, and the keel 5.2–5.5 mm (0.20–0.22 in) long. The stamens have white to pale green filaments 2.4–7 mm (0.094–0.276 in) long. Flowering occurs from June to February, and the fruit is a woody hairy, broadly elliptical pod 4.5–7 mm (0.18–0.28 in) long and 2.8–3.8 mm (0.11–0.15 in) wide.

This species of Jacksonia grows in shrubland on sand over laterite from north of Mingenew to Wongan Hills in the Avon Wheatbelt and Geraldton Sandplains bioregions of south-western Western Australia.