BRIEF DESCRIPTION: Amanita jacksonii has a brilliant red cap, 80 - 120 mm wide with an umbo and marginal striations taking up 40 - 50% of the radius.  The red pigment fades from margin toward the center with age.

The gills are free to narrowly adnate, moderately crowded to crowded, orange-yellow to yellow-orange to yellow.  The short gills are subtruncate to truncate.

The stem (90 - 140 x 9 - 16 mm) is yellow and is decorated with orange fibrils and patches that are the remnants of a felted extension of the limbus internus of the otherwise white volva.  In the center photo, a piece of the orange, felted material failed to separate from the margin of the yellow-orange annulus and is being peeled up the stem surface.  The volval sac is 40 - 70 mm high and up to 4 mm thick at its midheight.

The spores measure (7.0-) 7.8 - 9.8 (-12.1) x (5.2-) 5.8 - 7.5 (-8.7) µm and are broadly ellipsoid to ellipsoid (rarely subglobose or elongate) and inamyloid.  Clamps are common at bases of basidia.

The species occurs with oak and pine.  In Hidalgo, the species occurs in cloud forest of pine.

The range of this species extends from the Province of Quebec, Canada at least to the State of Hidalgo, Mexico.  The photograph in figure 92 of Guzmán and Ramírez-Guillén (2001) shows what appears to be A. jacksonii being sold in a public market in Guatemala.  Other Western Hemisphere species whose ranges overlap that of A. jacksonii in the "Slender Caesar group" include A. arkansana Rosen, A. banningiana Tulloss nom. prov., and A. murrilliana Singer.  In the US, A. jacksonii may be found throughout appropriate habitat east of the Great Plains.

The Slender Caesars are formally called stirps Hemibapha.  For more on classification of related taxa see A. caesarea (Scop. : Fr.) Pers. and A. hemibapha (Berk. & Broome) Sacc.  Amanita caesareoides Lyu. N. Vassilieva is a sister species from eastern Asia. -- R. E. Tulloss