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Dioon aculeatum Lem., Ill. Hort. 2. Misc. 92 (1855).
Two subspecies are recognised, Dioon edule subsp.
angustifolium representing the more northerly populations from
more xeric environments. The southerly populations here placed in subsp.
edule show a great deal of geographic variation, and future study
will probably recognise additional taxonomic entities.
D. edule from near the town of Palma Sola, Veracruz typically has slightly keeled leaves with slightly imbricate leaflets. D. edule near the city of Rio Verde, San Luis Potosi has typically flat leaves and leaflet insertion. The population of D. edule from the Rio Pescados drainage is essentially the same as the type locality at Chavarillo, Vercruz; large, long flat leaves with broad leaflets (Jeff Chemnick)
Distribution and habitat: Mexico - Nuevo Leon, San Luis, Tamaulipas (var. angustifolium)
Conservation status: 1997 IUCN Red List of Threatened Plants category R.
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Plants arborescent. Stem 4 m tall, 30-50 cm diam. 50-150 leaves in crown.
Leaves light or bright green or blue or blue-green, semiglossy to dull, 100-200 cm long, flat (not keeled) in section (opposing leaflets inserted at 180° on rachis), with 70-150 leaflets; basal leaflets reducing to spines, petiole spine-free for 5 cm.
Leaflets narrowly lanceolate, concolorous, not falcate, inserted at 90° to rachis, not overlapping; margins flat, entire; median leaflets 6-12 cm long, 5-10 mm wide.
Cataphylls 20-30 mm long, fawn tomentose.
Pollen cones ovoid to fusiform, pale brown, 15-40 cm long, 6-10 cm diam. Microsporophyll apex 30 mm long, 20 mm wide.
Seed cones ovoid, pale grey, 20-35 cm long, 12-20 cm diam. Megasporophyll apex 35 mm long, 25 mm wide.
Seeds ovoid, 25-45 mm long, 20-30 mm wide, sarcotesta cream or white.
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