Plants lack an internal tubal system

Non-vascular plants.

Explanation:

Non-vascular plants are those plants in which vascular system having xylem and phloem is absent. In these plants, an internal tubal system that transports water and other nutrients is absent and they possess simpler types of tissues for internal transport of minerals and water by osmosis or diffusion.

Thus, the correct word is to be filled in the blank is 'non-vascular.'

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