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Is there a plant (not a microscopic type but one that is visible to the naked eye) that has so much iron (or magnetite), cobalt, or nickel in its body that it can attract a magnet?
In this case "attract" would mean that a person holding a small magnet next to the plant can feel a small attraction between the magnet and the plant.
There was a 2011 study where they used a sensitive atomic magnetometer to try to detect a plant's magnetic field. They stated that:
To our knowledge, no one has yet detected the magnetic field from a plant. Biochemical processes, in the form of ionic flows and time varying ionic distributions, generate electrical currents and time-varying electric fields, both of which produce a magnetic field. However, contrasted to muscle contraction and brain processes, which have a characteristic time scale shorter than one second, plant bioprocesses span several minutes to several days and the expected magnetic field from such processes is correspondingly smaller.
Measurements with a sensitive atomic magnetometer were performed on the Titan arum (Amorphophallus titanum) inflorescence, known for its fast biochemical processes while blooming. We find that the magnetic field from these processes, projected along the Earth’s magnetic field, and measured at the surface of the plant, is < 0.6 lG.
So according to this, no, you wouldn't be able to sense the magnetic field from a plant with a magnet.
I would like to add from my random-seminar experience that there are magnetic bacteria, that orient along magnetic field due to magnetosomes, e.g. Magnetospirillum magnetotacticum. Please look into Wiki article. So one can imagine symbiotic association between plant and such bacteria.
More to OP's question, remember that any electric current (aka moving charges) creates magnetic field around it. If net charge of plant's xylem sap is non-zero than there will be magnetic field created when current flows. But it will be minuscule.
