Persoonia mollis is an erect to prostrate shrub that typically grows to a height of 0.2–5 m (7.9 in – 16 ft 4.9 in) and has smooth bark and young branchlets that are covered with greyish to rust-coloured hairs. The leaves are linear, oblong to lance-shaped or spatula-shaped, 15–120 mm (0.59–4.72 in) long, 0.8–17 mm (0.031–0.669 in) wide and much paler on the lower surface. The flowers are arranged in groups of up to thirty along a rachis up to 150 mm (5.9 in) long that grows into a leafy shoot after flowering, each flower on a pedicel about 1–3 mm (0.039–0.118 in) long, usually with a leaf at the base. The tepals are yellow, 8–11.5 mm (0.31–0.45 in) long and hairy on the outside. Flowering mostly occurs from late December to May and the fruit is a green drupe about 8 mm (0.31 in) long and 7 mm (0.28 in) wide.^[2][3][4][5]

Persoonia mollis was first formally described in 1810 by Robert Brown in Transactions of the Linnean Society of London.^[6][7]

In 1991, Siegfried Krauss and Lawrie Johnson described nine subspecies of P. mollis in the journal Telopea, and the names are accepted by the Australian Plant Census:

• Persoonia mollis subsp. budawangensis S.Krauss & L.A.S.Johnson^[8] is an erect shrub, 1.2–4 m (3 ft 11 in – 13 ft 1 in) tall with small, oblong leaves mostly 15–60 mm (0.59–2.36 in) long and 0.8–6 mm (0.031–0.236 in) wide and is endemic to the Budawang Range;^[4]
• Persoonia mollis subsp. caleyi (R.Br.) S.Krauss & L.A.S.Johnson^[9] is an erect shrub, 1.2–4 m (3 ft 11 in – 13 ft 1 in) tall with small, linear to narrow lance-shaped leaves 30–60 mm (1.2–2.4 in) long and less than 6 mm (0.24 in) wide;^[4]
• Persoonia mollis subsp. ledifolia (A.Cunn. ex Meisn.) S.Krauss & L.A.S.Johnson^[10] is an erect shrub, 1.2–4 m (3 ft 11 in – 13 ft 1 in) tall with small, oblong leaves mostly 20–40 mm (0.79–1.57 in) long and 0.8–6 mm (0.031–0.236 in) wide and is found between Fitzroy Falls and Kangaroo Valley;^[4]
• Persoonia mollis subsp. leptophylla S.Krauss & L.A.S.Johnson^[11] is a dense, compact shrub 0.8–1.5 m (2 ft 7 in – 4 ft 11 in) high with bright green, linear to thread-like leaves 0.8–1.5 mm (0.031–0.059 in) wide that are sparsely hairy on the lower surface;^[4]
• Persoonia mollis subsp. livens S.Krauss & L.A.S.Johnson^[12] is a dense, compact shrub 0.8–1.5 m (2 ft 7 in – 4 ft 11 in) high with green to greyish, linear to thread-like leaves 0.8–1.5 mm (0.031–0.059 in) wide that are densely hairy on the lower surface;^[4]
• Persoonia mollis subsp. maxima S.Krauss & L.A.S.Johnson^[13] has large, soft, lance-shaped leaves 40–80 mm (1.6–3.1 in) long and 6–17 mm (0.24–0.67 in) wide, the flower buds covered with copper-coloured hairs about 2–3 mm (0.079–0.118 in) long;^[4]
• Persoonia mollis R.Br. subsp. mollis^[14] has large, soft, lance-shaped leaves 40–80 mm (1.6–3.1 in) long and 6–17 mm (0.24–0.67 in) wide, the flower buds densely covered with whitish hairs about 1 mm (0.039 in) long;^[4]
• Persoonia mollis subsp. nectens S.Krauss & L.A.S.Johnson^[15] has large, pliable but not soft, lance-shaped leaves 40–80 mm (1.6–3.1 in) long and 6–17 mm (0.24–0.67 in) wide, and flower buds sparsely covered with whitish hairs about 0.5 mm (0.020 in) long;^[4]
• Persoonia mollis subsp. revoluta S.Krauss & L.A.S.Johnson^[16] is a prostrate, spreading shrub, 0.1–0.5 m (3.9 in – 1 ft 7.7 in) tall and up to 4 m (13 ft) wide, with oblong to egg-shaped leaves 30–60 mm (1.2–2.4 in) long and more than 6 mm (0.24 in) wide.^[4]

Soft geebung grows from heath to forest, usually on sandstone, from the Blue Mountains and Hawkesbury River south to the Clyde River.

• Subspecies budawangensis grows from woodland to forest and is endemic to the Budawang Range;^[17]
• Subspecies caleyi grows in forest between Jervis Bay and Durras Lake on the South Coast;^[18]
• Subspecies ledifolia occurs between Kangaloon, the Shoalhaven River, Jamberoo and Wingello where it grows from heath to forest on Hawkesbury Sandstone;^[19]
• Subspecies leptophylla is found between the Shoalhaven River, Budawang Range, Nerriga and Nowra and on the Beecroft Peninsula where it grows in heath and forest on Nowra and Conjola sandstones;^[20]
• Subspecies livens is found between Penrose, Goulburn and Braidwood, growing in woodland on metasedimentary rock and conglomerate;^[21]
• Subspecies maxima grows in forest on Hawkesbury sandstone in the Cowan-Hornsby area;^[22]
• Subspecies mollis is found in forest on sandstone in the Blue Mountains;^[23]
• Subspecies nectens occurs between Oakdale, Hill Top and the Illawarra Escarpment where it grows in forest;^[24]
• Subspecies revoluta grows in forest on Hawkesbury sandstone between Nattai Gorge, Bullio, Berrima and Canyonleigh.^[25]