Final answer:
Plants described as spindly and primitive include horsetails, bryophytes, certain gnetophytes like Welwitschia, and whisk ferns, which all have distinctive and ancient characteristics that provide them with a primitive morphology.
Step-by-step explanation:
The type of plant that is described as spindly and primitive looking could refer to various groups of plants, such as horsetails (Equisetum), bryophytes, gnetophytes, and certain ferns. Horsetails, with less than 20 species, have distinctive ribbed and jointed stems with scale-like leaves and thrive in damp environments. Bryophytes represent some of the earliest terrestrial plants and lack lignin, which makes them nonvascular and quite simple in appearance. Gnetophytes, such as Welwitschia, have unusual forms with some species producing only a pair of leaves, and they are closely related to angiosperms. Ferns, particularly whisk ferns, can also appear primitive due to their lack of roots and leaves, with photosynthesis occurring in their green stem.