Plants adapted to low light intensity have

• a larger photosynthetic unit size than the sun plants
• b higher rate of CO2 fixation than the sun plants
• c more extended root system
• d leaves modified to spines

As plants adapt, within life-cycle, to different average light intensity they adjust the quantities of pigment molecules to maximize photosynthetic capacity.

This study on canopy, gap, and understody plants in tropical forests ought to address many questions on the subject, full article should be available for free at that link.

In short, plants with more exposure to light on average have lower carotenoid content, larger xanthophyll cycle pools (mechanism for dealing with photoinhibition), and higher maximum photosystem output per unit time. As we move down the canopy, members of the same or similar species will reduce the size of the xanthophyll cycle pool, increase carotenoid content relative to chlorophyll content, and subsequently reduce maximum photosystem capacity.

This study doesn't specifically address it, but some varieties of plant will respond by increase available photosynthetic surface area - either by increasing relative pigment concentration in secondary receptive surfaces (petioles, stems, etc), or by expanding primary photosynthetic surface area, the specific mechanisms involved here vary widely so a concise generalization regarding 'will leaves grow larger' is not reasonable.