Spire trees are tall, thin, genetically-engineered relatives of cypress trees that evolved to inhabit the low-gravity and perpetual twilight of the Shadowland Bogs on Neo-Jalisco.   The low light levels of the tree's natural environment made its needles grow black, in order to absorb all available light.

They were engineered as living security devices, designed to repel or kill intruders on the grounds of the estates of minor nobility in the star kingdoms of the Sagittarius Rim.  Spire trees are sensitive to infrared, which allows them to detect intruders.  When this happens, special growths under the branches of the tree release clouds of a potent neurotoxin.  In small doses, the toxin induces nightmarish hallucinations.  At higher doses, it kills the victim.  Spire trees are generally planted as defensive windbreaks, so if an intruder gets too close, a small dose of toxin is released.  If this does not deter the intruder, the other trees in close proximity release enough of the agent that it should kill any vertebrate unprotected by full-environmental armor.