sentences:  The horsetail "Calamites" appeared in the Carboniferous.Unlike the modern horsetail "Equisetum", "Calamites" had a unifacial vascular cambium, allowing them to develop wood and grow to heights in excess of 10 m and to branch repeatedly.While the form of early trees was similar to that of today's, the Spermatophytes or seed plants, the group that contain all modern trees, had yet to evolve.