(A) are sensory antennae that sense approaching storms, causing the doors (B) to open. This releases the vine (I), which unfurls its kite-membrane (E) and inflates its gas bladder (D). The gas bladder raises the vine up to the point that the membrane can work to catch wind. When lightning strikes the vine, the current passes through processor (J), where it is harnessed and converted into chemical energy. The vine may also harness and store energy, but probably only once per release. The "roots" (L) ground the plant and allow the current to escape in a diffuse way.
The pili (C) have a dual function. After the storm, as the vine descends, they sequentially attach to opposing pili on the vine, pulling it in and causing it to fold and pack into the holding bulb in a predetermined way. Once this is accomplished, the pili become channels for the transfer of nutrients from the vine (and from the processor through the vine). Since the vine also attaches to itself and must fill a three-dimensional space, nutrients may pass from section to section of the vine before finally being absorbed by the bulb wall (H) and stored in the food pockets (F).
To protect the bulb wall (the main living tissue of the plant) from errant discharges, the plant secretes insulation (K) and (M). Even in adulthood, the plant retains some decomposer/parasitic roots (G), which also gather water. Because it has enormous energy stores that it must live off of between strikes (it may be a year before it is able to capture another), the bulb wall (H) must be very strong to deter herbivores, bacteria, fungi, and parasites. The food pockets (F) store food largely as elemental magnesium, which has very high energy density, making it an efficient storage medium. Of course it must be kept in very low-oxygen conditions and the bulb wall also protects against air.
On the planet that these plants were found on, one can stand outside during a thunderstorm and be safe from all strikes because the towering vines will capture and trap them all. The lightning plants also protect forests of shorter bladder-vines, which consume sunlight in the usual way. When it was discovered that the plants store food as magnesium, one speculator - on a hunch - bought up all the land on the planet where there was better than even odds that coal would be found. As it turns out, the coal on the planet (being composed of compressed, long-dead plants) is unusually rich in magnesium. The speculator made trillions.
This is a closeup of the kite-membrane and gas bladder at the end of the vine. The gas bladder inflates during storms and deflates when the vine is retracted. The kite-membrane unfurls during storms and is wrapped around the vine when the vine is retracted. I'm not sure how this would work. Perhaps there is a spring mechanism or musculature.