I have not opened Dwarf Fortress in a while, so I based this off of the Dwarf Fortress wiki: http://dwarffortresswiki.org/index.php/DF2014:Crop

Considerations for each:
Cave wheat:
    Seeds are called "seeds", therefore plant.
    White plant tile, dark yellow seed tile - I could not easily draw the stalks white, so instead the seeds are whiter on my plant image than on my seed image. Perhaps the seeds become discolored and darker when they are disconnected from the plant.
    PREFSTRING: (liked for its) "stalks" - so a wheat-like structure fits.

Quarry bush:
    Seeds are called "nuts", therefore plant.
    Light gray plant tile, white seed tile.
    PREFSTRING: (liked for its) "gray leaves" - so with explicit leaves.

Pig tail:
    Seeds are called "seeds", therefore plant.
    Light gray plant tile, dark gray seed tile, however there are no gray colors in the palette of this challenge, so I drew them as a brown-cyan mix.
    PREFSTRING: (liked for its) "twisting stalks" - the eponymous pig tails. I once thought the pig tails would be the roots instead.

Plump helmet:
    Seeds are called "spawn", therefore fungus.
    Purple plant tile, red seed tile. The plant tile is the spade symbol, which looks like a normal mushroom cap.
    PREFSTRING: (liked for its) "rounded tops". I looked this up when I was already done, and there was too little time to go back to make them rounder, alas.

Dimple cup:
    Seeds are called "spawn", therefore fungus.
    Blue plant tile, magenta seed tile - I draw the stem of the mature form pink like the spawn, so the blue growths usable for blue pigment only appear in a mature Dimple Cup. The plant tile is the heart symbol, so it was drawn as an oddly shaped fungus.
    PREFSTRING: (liked for its) "soothing color".

Sweet pod:
    Seeds are called "seeds", therefore plant.
    Red plant tile, green seed tile.
    PREFSTRING: (liked for its) "round shape". Sweet Pod is a pun on seed pod, so the image should show that. I tried drawing the plant so the green seeds would be visible (as in the seed pod of a lotus), but I could not make it look good and was almost out of time.

Gecimen: Thank you! The table made me struggle a bit with the available colors but it worked out alright, I think.

redmilion: ¡Gracias!

SmAshMk01: Thank you! It was inspired slightly by https://www.youtube.com/watch?v=rPf90hqCKHg

specialmin64: Thank you! Indeed it could have used more refinement, but I submitted it 3 minutes before deadline. I like Barlowe's hell, I guess it is similar (eg the floating fantasy letters).

DustfingerPT: Thank you!

Flinigan: Thank you! I like descriptive titles. I hope to participate in more challenges.

vrine: Thank you!

Hapiel: Thank you!

Sarahboev: Thank you!

MrQuetch: Thank you! I am also happy with the colors, I believe it benefitted from 3 clearly seperate color ramps, 2 of which are very simple (8 colors in black → brown → light blue ramp, 3 colors in red ramp, 3 colors in green ramp); with more complex palettes (where the colors do not organize into a small number of discrete ramps) the colors often blend together more and look less distinct.