Paul K. Strother, Said Al-Hajri, Alfred Traverse; New evidence for land plants from the lower Middle Ordovician of Saudi Arabia. Geology ; 24 (1): 55–58. doi: https://doi.org/10.1130/0091-7613(1996)024<0055:NEFLPF>2.3.CO;2
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Macerations of Middle Ordovician (Llanvirnian) shales from Saudi Arabia yield an assemblage of spores of probable land plants (cryptospores), acritarchs, and chitinozoa. The production of sporopollenin-containing, sporelike tetrads is considered a fundamental character of the embryophytes, because no extant algae produce spores of this type. No trilete spores were found at this horizon, reinforcing previous assertions that obligate meiotic tetrads predate the earliest trilete spores. Sporomorph tetrads and dyads, in conjunction with cuticlelike fragments, were probably derived from terrestrial plants at a bryophyte grade. Although there are reports of possibly older cryptospores, the Hanadir assemblage described herein clearly establishes their presence by Llanvirnian time.