The greenish, creamy white flower of Pterygodium pentherianum is sweetly scented and shallowly hooded. The inner margins of the lateral petals are overlapped by the dorsal sepal. The lateral sepals are concave with acutely pointed tips. The broadly oblique lateral petals have crenate outer margins.
The diverging, rounded lip lobes sometimes have a small central tooth pointing down between them, absent from the fork in the lip of the flower in picture. The erect lip appendage in the flower centre is broad and fleshy, ending in three lobes at its tip.
Flower dimensions are about 25 mm by 15 mm (Liltved and Johnson, 2012; Manning and Goldblatt, 1997; Bond and Goldblatt, 1984; iNaturalist).