Paulliniamartinellii is unique within the genus by its large (3–5 cm long), membranaceous, clasping stipules and overlapping cataphylls and by the large (ca. 1 cm long), overlapping, boat-shaped bracts, resembling no other species of Paullinia.

BRAZIL. Pará; Mun. Oriximiná, Rio Caxipacoró, km 72 on the road north of Cachoeira Porteira, along disturbed roadside, 30 Jun 1980 (fl, fr), Davidson & Martinelli 10661 (holotype US!; isotypes INPA!, NY!).

Liana. Stems furrowed and tomentulose when young, becoming glabrous, terete and lenticellate with age; cross-section simple; xylem with wide rays and phloem wedges. Tendrils similar to those in other Paullinia but not associated with inflorescences. Cataphylls overlapping, similar to stipules in size and texture, produced at base of lateral branches. Stipules foliaceous, membranaceous, ovate to cordiform, clasping the stem, 3–5 × 2–4 cm, puberulous, conspicuously veined, with undulate margins. Leaves pinnately 5-foliolate; petiole and rachis nearly terete, adaxially furrowed, tomentose or tomentulose; petiole 14.5–16.5 cm long, pulvinate at base; rachis 6–8.5 cm long; petiolules pulvinate, tomentulose, distal petiolule ca. 1 cm long, lateral petiolules 2–5 mm long; leaflets membranaceous with linear punctations, glabrous except veins tomentulose on adaxial surface and puberulent on abaxial surface, acuminate at apex, margins dentate or subentire, with secondary veins projecting as glandular teeth; venation craspedodromous, abaxially prominent; tertiary venation reticulate-percurrent between the secondary veins; distal leaflet 24–25 × 12–15.5 cm, broadly elliptic to obovate, attenuate at base; lateral leaflets 15–18 × 9–11 cm, oblong to ovate, rounded or sub-cordate at base. Thyrses cauliflorous, lacking tendrils, in fascicles of 5–7; axes robust, woody, 20–34 cm long, ferruginous-tomentose; bracts ovate concave, crustose, 8–10 × 6–8 mm, minutely sericeous; cincinni 2- or 3-flowered, sessile; bracteoles broadly elliptic, concave, tomentulose, ca. 5 mm long, covering the cincinnus; pedicels articulate at base. Sepals 4, sericeous tomentose, crustose, the outer sepals ovate, ca. 5 mm long, inner sepals broadly elliptic, concave, 5.5–6 mm long, anterior sepal emarginate; petals obovate, ca. 6.5 mm long, abaxially covered with glandular trichomes; appendages hood-shaped, ca. 5 mm long, with fleshy, yellow, corniform crests, two in posterior appendages, one in anterior appendages; nectary 4-lobed, posterior lobes rectangular with emarginate or truncate apex, anterior lobes triangular; torus villose; filaments connate at base, lanate throughout, 2–3 mm long; anthers glabrous. Capsule (immature) ellipsoid, unwinged, orange, ferruginous-hirtellous, long-attenuate at base, and obtuse and apiculate at apex.

Terra firme forest at elevations below 100 m.

Old flowers and young fruits known from June–July.

The specific epithet honours Dr. Gustavo Martinelli, eminent Brazilian botanist at Rio de Janeiro Botanical Garden, who made the first collection of this species.

Known from three collections from two localities with an EOO of ca. 3,000 km² in the Municipality of Oriximiná in the state of Pará, Brazil. The new species seems to be rare and, because of its small known EOO, it is here treated as vulnerable (VU) within IUCN guidelines.

BRAZIL. Pará; Mun. Oriximiná, Estrada da Cachoeira Porteira km 72, próximo ao igarapé Caxicoporó, margem esquerda, mata firme, solo argiloso, 1 Jul 1980 (fl), Cid Ferreira et al. 1223 (INPA), Rio Cachorro, Cachoeira de Varador, terra firme forest, 90 m elev., 22 Jun 1980 (fl, fr), Martinelli & Davidson 7158 (MG, NY, RB).

Paulliniamartinellii is the only species within the genus known to have large (3–5 cm long), membranaceous, clasping stipules and large (ca. 1 cm long), overlapping, boat-shaped bracts. Its position within the genus has not been ascertained as no adequate material is available for carpological or molecular analyses.