  Galactic haloes in a $\Lambda$-CDM universe are predicted to host today a
swarm of debris resulting from cannibalised dwarf galaxies. The chemo-dynamical
information recorded in their stellar populations helps elucidate their nature,
constraining the assembly history of the Galaxy. Using data from APOGEE and
\textit{Gaia}, we examine the chemical properties of various halo
substructures, considering elements that sample various nucleosynthetic
pathways. The systems studied are Heracles, \textit{Gaia}-Enceladus/Sausage
(GES), the Helmi stream, Sequoia, Thamnos, Aleph, LMS-1, Arjuna, I'itoi, Nyx,
Icarus, and Pontus. Abundance patterns of all substructures are cross-compared
in a statistically robust fashion. Our main findings include: {\it i)} the
chemical properties of most substructures studied match qualitatively those of
dwarf Milky Way satellites, such as the Sagittarius dSph. Exceptions are Nyx
and Aleph, which are chemically similar to disc stars, implying that these
substructures were likely formed \textit{in situ}; {\it ii)} Heracles differs
chemically from {\it in situ} populations such as Aurora and its inner halo
counterparts in a statistically significant way. The differences suggest that
the star formation rate was lower in Heracles than in the early Milky Way; {\it
iii)} the chemistry of Arjuna, LMS-1, and I'itoi is indistinguishable from that
of GES, suggesting a possible common origin; {\it iv)} all three Sequoia
samples studied are qualitatively similar. However, only two of those samples
present chemistry that is consistent with GES in a statistically significant
fashion; {\it v)} the abundance patterns of the Helmi stream and Thamnos are
different from all other halo substructures.
