Opuntia engelmannii and O. lindheimeri, have undeniable similarities, but there are also constant differences. We accept these taxa as separate and distinct species. However, Opuntia lindheimeri has been described as a variety of O. engelmannii by some authors. However you think of them, this checklist describes the differences.
- The younger pads of O. lindheimeri are less woody and “softer” or “greener” in appearance.
- O. lindheimeri spines are yellow, or range to shades of orange-yellow or may have reddish hues. O. engelmannii spines range from white, to tan, to yellow shades and brownish. O. engelmannii spines are seldom a rich canary yellow or shiny yellow. If yellow, O. engelmannii spines are dull yellow. O. lindheimeri spines are almost shiny, whereas O. engelmannii spines are chalky.
O. engelmannii spines are typically darker at the base than O. lindheimeri spines. The base of O. engelmannii spines may be brown, or blackish, or even dark red-brown. Occassionally, plants are found with spine bases that are not darker than the spines. In contrast, the base of O. lindheimeri spines are seldom true brown or black but may be red-brown, dark plum, rust-brown, pink shades, or dark yellow.
- The annular markings of O. lindheimeri spines are more apparent than in O. engelmannii. The markings may not even be observable in O. engelmannii.
- O. lindheimeri fruits are narrower at the base or even vaguely pear-shaped; they tend to have a smooth surface and are typically red when ripe newly ripe. O. engelmannii fruits are oval or roundish, darker and less red in color, and with a more rugose surface; the umbilicus is usually more depressed into the end of fresh fruit. Glochids may or may not be present on either fruit type.
- Plants with orange or red flowers occur occasionally (not often) in O. lindheimeri but are rare in O. engelmannii. Yellow flowers of either species may change to orange shades late in the day of anthesis or on the day after.
- O. engelmannii fruits are sweet and pleasant tasting, whereas those of O. lindheimeri are sour and not sweet. O. lindheimeri fruits are sometimes almost noxious.
- O. lindheimeri is primarily a plant of Texas east of the Pecos River (extending into LA). In contrast O. engelmannii is typically found west of the Pecos River to CA. If west of the Pecos River, O. lindheimeri grows in more mesic conditions than O. engelmannii such as valley bottoms or partially shaded slopes.