The net carbs in leeks is about 12, and broccoli about 4 or 5 - that is from memory so only approximately.
The higher figures, 14 and 7 are the carbs including the fibre, and the lower ones are wrong.
There are very few vegetables which are so low in carbs and using that information could be very dangerous.
The edible parts of leeks are the leaves - usually the blanched lower parts, so they are not really below ground plants, as the blanching could be done with anything which excludes light.
Although a bit high for me I have used them sparingly for flavour, or to replace pasta sheets.