The following new species of pyrenocarpous lichens are described from Rondônia: Agonimia tenuiloba: corticolous, thallus with minute flabellate lobes developing goniocysts; ascomata smooth, grey, ellipsoidal; ascospores densely muriform, 30–50(–76)×20–35 µm. Anisomeridium lateriticum: saxicolous; conidiomata sessile, pyriform, ostiole with brown and hyaline septate setae; conidia simple to 1-septate, 8–11×2·0–2·5 µm. Anisomeridium triseptatum: corticolous, ascomata with lateral ostioles; ascospores (1–)3-septate, 25–30×7·5–10·0 µm, often with gelatinous appendages. Mycomicrothelia megaspora: ascospores ornamented, 1-septate, (27–)29–35(–40)×8–12 µm, often with a gelatinous layer 6–15 µm thick. Porina linearispora: corticolous; thallus green, shiny; ascomata immersed, 0·2–0·3 mm; ascospores filiform, (7–)9(–13)-septate, 75–90×1·5–2·0 µm. Porina maxispora: corticolous; thallus green, matt; ascomata immersed, 0·5–0·7 mm; ascospores filiform, (17–)23–35-septate, 95–110×4·5–5·5 µm. Porina novemseptatoides: saxicolous; thallus very thin, brown, glossy; ascomata superficial, 0·1–0·2 mm; ascospores fusiform, (7–)9-septate, 21–24×4·5–5·0 µm, with a c. 5 µm thick gelatinous layer. Porina termitophila: terricolous; thallus greyish green; ascomata emergent, 0·15–0·20 mm; ascospores fusiform, 1–3-septate, 13–15×2·5–3·0 µm. Pyrenula bispora: corticolous, thallus whitish, ascomata dispersed; hamathecium inspersed; ascospores 2 per ascus, muriform, 55–75×19–23 µm. Pyrenula leptaleoides: corticolous; thallus green to pale brown; ascomata deeply immersed in bark, with long necks fused in joint ostioles visible as brown dots on the surface; ascospores 23–27×8–11 µm, with rather angular lumina. Pyrenula rhomboidea: corticolous; thallus olive-brown; ascomata single, immersed; ascospores irregularly uniseriate, clavate-rhomboidal, 11–13×3·5–4·0 µm.

A key is provided to all species of pyrenocarpous lichens (except Trypetheliaceae) found in Rondônia. Nearly all species are new reports for Rondônia. Aspidothelium glabrum, Pyrenula leucotrypa and P. micheneri are newly reported for South America. The usually foliicolous Strigula nitidula is reported for the first time from bark.

The high lichen diversity is explained by the poor soils, supporting an only moderately dense forest where enough light can reach the tree trunks at ground level to support a rich flora of crustose lichens usually confined to the upper trunks.

Arthopyrenia tuscanensis Coppins & S. Ravera and A. coppinsii S. Ravera are described as new to science. They share the characteristic tadpole-shaped ascospores with a conical lower cell, but are otherwise comparable to A. salicis A. Massal.