Anatomy of Eriocaulaceae

Anatomy of Eriocaulaceae

All Eriocaulaceae species present roots with one-layered epidermis, endodermis with thick-walled cells, one-layered pericycle, and a vascular cylinder without pith. The steams have collateral cortical vascular bundles, one-layered endodermis and pericyle, and a vascular cylinder with amphivasal bundles and pith. The leaves present long epidermal cells in frontal view, with paracitic stomata only on abaxial surface. In cross section, the epidermis is one-layered. The mesophyll is composed of 1-2 layers of palisade chlorenchyma facing the adaxial surface and multi layers of spongy chlorenchyma facing both the adaxial and abaxial sufaces. It is interrupted by the bundle sheath extensions. The vascular bundles are collateral and have a double sheath: the outer one of endodermic origin and the inner one of pericyclic origin. The scapes have a polygonal form, with epidermis and endodermis one-layered, sinuous perycicle, central cylinder with collateral vascular bundles and pith. Only Paepalanthus subg. Thelxinöe does not have scape. The flowers characters are useful at infrafamiliar level. The staminate flowers of Eriocauloideae present a diplostemonous androecium with six stames, and those of Paepalantoideae present an isostemonous androecium with three stamens and three scalelike staminodes. The pistillate flowers of Eriocauloideae present three simple styles while those of Paepalanthoideae present three simple styles alternated with three nectariferous appendages. Both the styles of Eriocauloideae and the nectariferous appendages of Paepalanthoideae are vascularized by the dorsal carpellary bundles. The embryological features are uniform for the family and consist of: endothecium with baseplate thickenings, microsporocytes directly derived from the sporogenous cells, spiraperturate pollen, ovules orthotropus, tenuinucellate, and bitegmic, with a micropyle formed by the inner integument, and antipodes arranged in a conspicuous cyst. The fruits are loculicidal capsules with a thin pericarp. The seeds are endotestal, with a micropilar operculum, and present an undifferentiated embryo and starchy endosperm.

Roots and stems – The variable anatomical characters in roots and stems of Eriocaulaceae are more related to environmental factors than to the taxonomic position of the species. Then, they are not useful for delimiting taxonomic groups.

Leaves and scapes – Some anatomical features can differentiate the taxa. One example is the specialized substomatal chambers that constitute an efficient structure for air exchange and present different patterns. In Comanthera subg. Thysanocephalus these chambers are composed of thick-walled cells that in longitudinal section have a “trabecula” shape. In Actinocephalus these thick-walled cells are short and long in cross section, and in longitudinal section they present a “T” shape, while in Leiothrix subg. Calycocephalus sect. Glabrae and Paepalanthus subg. Paepalocephalus subsect. Aphorocaulon they have a “U” shape. Other anatomical leaf structures, as epidermis with thick-walled cells, mesophyll with hypodermis, collenchymatous and sclerenchymatous bundle sheath extensions, and numerous vascular bundles group Leiothrix, Comanthera subg. Thysanocephalus, Comanthera subg. Comanthera, and Paepalanthus subg. Platycaulon. In the same way, the presence of epidermis with thin-walled cells, mesophyll with parenchymatous bundle sheath extensions, and loosely aggregated chlorenchyma is shared by Eriocaulon, Syngonanthus sect. Carpocephalus, S. sect. Syngonanthus, and Tonina.

Flowers - The scalelike staminodes present in Actinocephalus, Comanthera, Lachnocaulon, Leiothrix, Paepalanthus, Rondonanthus, Syngonanthus, and Tonina (Paepalanthoideae) probably indicate a reduction of the outer whorl of stamens, which are present in Eriocaulon and Mesanthemum (Eriocauloideae). The occurrence of pistillodes in staminate flowers and stylar appendages in pistillate flowers of Paepalantoideae are emphasized as nectariferous structures in Eriocaulaceae.

Seeds – The seed coat structure is uniform in origin and is a consistent taxonomic character for the family. In Comanthera, Lachnocaulon, Paepalanthus, Syngonanthus, and Tonina for example, the sculptures of the endotesta provide the seeds with a rib-like appearance that is less noticeable in some species of Eriocaulon.

Figures 1-6. Roots (Figs. 1-3) and stems (Figs. 4-6) of Eriocaulaceae species in cross sections. Fig. 1. Comanthera suberosa. Figs. 2-3. Eriocaulon elichrysoides. Figs. 4-6. Actinocephalus denudatus (arrow=adventitious root; E=epidermis; En=endodermis; P=pericycle; TF=leaf trace) (Fig. 1-bar=25 µm; Figs. 2-3-bar=70 µm; Figs. 4-5-bar=80 µm; Fig. 6-bar=200 µm).

Figures 7-14. Leaves of Eriocaulaceae species in cross (Figs. 7-8, 10-13) and longitudinal (Figs. 9, 14) sections. Fig. 7. Comanthera brunnea. Fig. 8. Detail of the stomata of C. linearis. Fig. 9. Detail of the stomata of C. magnifica. Figs. 10-11. C. cipoensis, detail of the stomata with specialized substomatal chamber (Fig. 11). Fig. 12. Syngonanthus verticillatus. Fig. 13. Actinocephalus polyanthus. Fig. 14. A. ramosus, detail of the specialized substomatal chamber (arrow=T-shaped cell; ES=stomata; CS=substomatal chamber) (Fig. 7-bar=50 µm; Figs. 8-9-bar=25 µm; Figs. 10, 12, 13-bar= 80 µm; Fig. 11-bar=10 µm; Fig. 14-bar=30 µm).

Figures 15-19. Leaves and scapes of Eriocaulaceae species in cross sections. Fig. 15. Comanthera cipoensis. Fig. 16. Paepalanthus chiquitensis. Fig. 17. C. caracensis. Fig. 18. P. flaccidus. Fig. 19. Syngonanthus anthemidiflorus (Figs. 15, 19-bar=100 µm; Figs. 16, 18-bar=50 µm; Fig.17-bar=80 µm).

Figures 20-30. Flowers of Eriocaulaceae species. Figs. 20-21. Eriocaulon elichrysoides: staminate (Fig. 20; arrow=pistillades nectariferous) and pistillate flower (Figs. 21; arrow=gynophore). Figs. 22-23. Syngonanthus caulescens: staminate (Fig. 22; arrow=nectariferous pistillodes) and pistillate flower (Fig. 23; S=stigma; SS=scalelike; NA=nectariferous appendage). Fig. 24. E. elichrysoides, Scanning electron micrography of the pistillate flower. Fig. 25. Paepalanthus flaccidus, SEM of the pistillate flower. Fig. 26. Actinocephalus polyanthus, staminate flower in longitudinal section. Figs. 27-28. P. scirpeum, anther in cross section (Fig.27) and ovule in longitudinal section (Fig. 28). Fig. 29. Leiothrix fluitans, SEM of the staminate flower Fig. 30. Lachnocaulon anceps, SEM of the pollen grain (Fig. 24-bar=30 µm; Figs. 25, 29-bar=100 µm; Fig. 26-bar=60 µm; Fig. 27-bar=25 µm; Fig. 28-bar=15 µm; Fig. 30-bar=10 µm).

Figures 31-38. Fruits and seeds of Eriocaulaceae species. Figs. 31-32. Syngonanthus hoffmannseggii, fruit and seeds in cross (Fig. 31) and longitudinal section (Fig. 32). Figs. 33-34. Scanning electron micrography of the seed of Eriocaulon kunthii and Comanthera cipoensis, respectively (arrow=operculum). Fig. 35. Paepalanthus scleranthus, seed in longitudinal section. Fig. 36. P. subtilis, unripe fruit and seed in cross section (asterisks=cuticle; tg=tegmen; ts=testa). Fig. 37. Leiothrix flavescens, seed in longitudinal section. Fig. 38. E. kunthii, SEM of the micropilar region showing the operculum (Fig. 31-bar=70 µm; Fig.32-bar=10 µm; Fig. 33-bar=152 µm; Fig. 34-bar=100 µm; Fig. 35-bar=25 µm; Fig. 36-bar=20 µm; Fig. 37-bar=30 µm; Fig. 38-bar=50 µm).

By Dr Vera Lucia Scatena

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith