| 1. Perianth parts 36 mm, stamens = or > perianth |
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| 2. Inflorescence a well developed panicle; flowers of main axis bisexual; flowers of branches often staminate; stamens 12 mm > perianth |
| Z. paniculatus |
| 2' Inflorescence raceme-like (rarely branched below); flowers all bisexual; stamens ± = perianth |
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| 3. Plant scabrous; inflorescence widely conic, pedicels 1540 mm, spreading; perianth parts short-clawed |
| Z. micranthus var. micranthus |
| 3' Plant glabrous; inflorescence narrowly conic, pedicels 612 mm, ascending; perianth parts long-clawed |
| Z. venenosus var. venenosus |
| 1' Perianth parts 515 mm, stamens < perianth |
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| 4. Perianth parts 58 mm pedicels spreading |
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| 5. Pedicels not upturned at tip; styles widely spreading or recurved; Mojave Desert, Tehachapi Mountain Area, Western Transverse Ranges |
| Z. brevibracteatus |
| 5' Pedicels upturned at tip; styles erect; wet soils, North Coast Ranges, Central Western California |
| Z. micranthus var. fontanus |
| 4' Perianth parts 815 mm |
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| 6. Flowers of lower inflorescence branches staminate; perianth parts 812 mm, ovate, obtuse, stamens 2/33/4 perianth length; Sierra Nevada |
| Z. exaltatus |
| 6' Flowers bisexual; perianth parts 815 mm, lanceolate to ovate, acute, stamens ± 1/2 length parts; w California |
| Z. fremontii
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