Manasynthesis

I have had a few of these for my Chalice World setting but the venerable TBone issued a challenge so here is my response and a listing of plants that rely on mana for energy instead of light.
Unless noted otherwise the ambient energy they gather is not large enough to affect the local mana level. They do tend to grow better in areas of higher mana levels and along dragon or ley lines.

Mage Moss

This white moss grows in thick clumps and sheets, particularly in damp and dark conditions. It is valued by alchemists as its easily harvested and ground up for use as a base in potions.

Mage Stools

This fungus sprouts quickly in areas where mages have recently cast multiple spells. The turbulence in local mana from frequent spell casting seems to be especially friendly to this fungus. They are a serious problem for spell casters and cause a -1 penalty to normal casting and a -5 penalty to ceremonial casting, including enchantment. They are also highly resistant to spells and enjoy a +5 resistance to regular spells cast on them.

Glow Flowers

These flowers come in many varieties and use some of the mana they gather to attract insects and other animals. This helps spread their pollen to other caves.  The light they provide is pretty dim, each flower is about a candles brightness but a cavern full of them can add up. Dwarves and other subterranean dwellers will breed them in a variety of colors and plant them as decorative background lighting.

Fae Bane

This is a parasitical plant, much like a hyperactive mistletoe and is a threat to magical creatures. Once in contact it slowly siphons off innate magic draining 1 point a minute from magical ERs and making casting very painful (treat as Agony). It requires little water or nutrients from soil and can live for days off a magical source even if uprooted.  Used by some to shackle mages.