(ˈ)āˈthaləməs adjective
Etymology: a- (II) + Latin thalam us marriage bed, bedroom (from Greek thalamos bedroom, room) + English -ous; akin to Greek tholos rotunda — more at dale
1. : lacking a torus or receptacle
athalamous flowers
2. : without apothecia, beds, or shields for spores
athalamous lichens