Numerical analysis of the lengths and positions of the two basal bodies (BBs), lamellar strip (LS) and anterior mitochondrion (AM) relative to each other in mid- and late-stage spermatids of mosses and liverworts reveals the existence of several well denned, but previously unrecognized, features which clearly distinguish the blepharoplasts of the two groups. The ten possible quotients were calculated from measurements of anterior BB lengths, posterior BB lengths, LS lengths, distances between the anterior tips of the BBs and distances between the transition regions of the BBs in mid-stage spermatids of 9 mosses and 16 hepatics. These critical data may be quickly compiled from a small number of electron micrographs. A Mann-Whitney rank order t test showed highly significant differences in 6 of the 10 quotients between the moss and liverwort taxa. The primary data for late-stage spermatids (4 mosses, 6 liverworts) also included the length of the AM. A Wilcoxon signed rank procedure revealed that the relationship between the AM and other blepharoplast components changed significantly between mid- and late-stage spermatids in mosses but not in liverworts. The clear-cut numerical differences between the blepharoplast components in each group are related to different patterns of development namely (1) bidirectional assembly of the LS in young spermatids of liverworts versus unidirectional (anterior) elongation at the same stage in mosses (2) elongation of the posterior BB over the nucleus in mid-stage spermatids of mosses and (3) maturational elongation of the AM in mosses. Since the differences between the blepharoplasts of mosses and liverworts become apparent only during the later stages in ontogeny and since the mode of development of basal body stagger, involving the same precisely defined patterns of proximal triplet microtubule extension, is unique to mosses and liverworts, we suggest that the two groups share a common ancestry.
The blepharoplasts of all the taxa used in the calculations are illustrated in a simplified form and the ‘average’ blepharoplast for mid- and late-stage spermatids of both mosses and liverworts is reconstructed from all the data presently available on the two groups. The same analysis of the blepharoplasts of hornworts, birlagellate lycopods, and charophytes highlights the differences between these groups and mosses and liverworts. Most striking is the side-by-side orientation of the basal bodies in hornworts and charophytes compared with the staggered arrangement in mosses, liverworts and the lycopods.