Maror

Is there any basis whatsoever for a seder plate having spots for both "maror" and "chazeres"? (Even leaving aside that the Mishnah Brurah paskens that chazeres is the best type of maror to use).

Update:

It was shown to me that this instruction appears in the commentary on the haggadah by the last Lubavitcher Rebbe. He gives two reasons for using both types: firstly, a lack of absolute certainty that chazeres is what we think it is, so that it makes sense to hedge our bets, and additionally due to kabbalistic reasons connecting horseradish to the straight-up maror and lettuce to koreich.

Subsequently, another source was shown to me that attributes the presence of both horseradish and chazeres on the seder plate to the Arizal. Rabbi Sholom Dovber Schneerson (the Rebbe Rashab) explains that the Arizal's arrangements of items on the seder plate highlights their connection to the eser sefiros:

z'roa - chesed - kindness, epitomized by Hashem's z'roa netuya in taking us out of Egypt.
beitzah - gevurah - strength - egg is cooked until it becomes hard.
maror - tif'eres - empathy - maror is a method through which we empathize with the Jews who suffered in Egypt.
These three constitute one subset of sefiros and are grouped into one triangle.

charoses - netzach - endurance - mortar symbolizes permanence
karpas - hod - humility - grows close to the ground
chazeres - y'sod - foundation? - chazeres joins together with matza in koreich
These three constitute a second subset of sefiros and a second triangle.

Malchus - dignity - is represented by the seder plate itself, and the three matzos placed below symbolize the three sefiros elyonos, chochma, bina, and da'as.

This, at least, answers my question regarding the source of the practice. Note to self: "When in doubt, attribute it to the Arizal" works surprisingly often.