176 



PHYLUM TRACHEOPHYTA: 



mostly equal-forking to approaching a straight main 

 stem; leaves commonly under 1 inch, eligulate, and 

 usually spiralled on stem (but also whorled, opposite, 

 or alternate, and sometimes in rows); leaves range 

 from scale-like to needle-like but generally over X- 

 inch long; roots form along creeping stems or grow 

 dovk'n from erect stems; most sporangia are on leaves 

 that are either organized into cones or are ungrouped 

 leaves that may be confined to "fertile areas" or scat- 

 tered on the sporophyte; one spore type, the spore 

 developing into a vaguely carrot-like, /g- to X-irich 

 gametophyte bearing both male and female sex or- 

 gans (Figures 11.10 and 11.11). 



MALE 

 GAMETOPHYTE 



Figure 11.8 Selaginello, two species of spike mosses; habit (about 

 natural size); brancfies (x 3); sporangium-bearing and vegetative leaves 

 (enlarged); c, cone; I., leaf; ms., leaf-bearing sporangium tliot forms 

 female spores; rp., rhizophore. (Used by permission, from Artfiur 

 Cronquist, /n(roduc(ory 8o(ony, Harper, New York, 1961.) 



Figure 11.9 Life cycle of Selaginella: e., egg; g.s., germinating 

 sporophyte; z., zygote. (Used by permission, from Arthur Cronquist, 

 Introductory Botany, Harper, New York, 1961.) 



Subphylum SPHENOPSIDA ( = ARTHROPSIDA; 

 CALAMOPSIDA) (Horsetails and 

 Scouring Rushes) 



Diagnosis: definite fossils date back to Middle 

 Devonian; most fossils resemble the single, living 

 genus, Eqmselum; living species are perennial herbs 

 with microphylls, but some fossils had leaves with 

 branched veins (macrophylls); stems are ribbed, 

 simple or branched, jointed, and have distinct nodes 

 and elongate internodes; roots are present; the leaves 

 are never alternate, but leaves and branches alternate 

 with one another at the nodes; sporangia are in cones 

 organized from specialized stalks; spores of one kind 

 (includes Eqmselum), or rarely two kinds (some fos- 

 sils); both sporophyte and gametophyte are func- 

 tionally independent at maturity; living gameto- 

 phytes are inconspicuous and have both sex organs on 

 the same plant (probably were on separate plants in 

 two-spore fossils) (Figure 11.12). 



Occurrence: about 20 living species in the genus 

 Equiselum of the order Equisetales; almost cosmopoli- 

 tan, but not in Australia; mostly in wet areas, also 

 shallow water emergents to well-drained soil. 



