Embryology of Siparunaceae (Laurales): characteristics and character evolution

Abstract

Embryological characters of Siparunaceae, which are poorly understood, were studied on the basis of two constituent genera, an African Glossocalyx and a South American Siparuna, to better understand their evolution within Laurales. These two genera have many embryological characteristics in common with the other lauralean families. Noticeably, they share the multi-celled ovule archesporium (uncertain in Glossocalyx) as a synapomorphy with all the other lauralean families except Lauraceae, the anthers dehisced by valves as a synspomorphy with all the other lauralean families except Calycanthaceae and Monimiaceae, and the bisporangiate anther as a synapomorphy with Gomortegaceae and Atherospermataceae. Siparunaceae are, however, distinct from all other laularean families in having unitegmic ovules that were derived from bitegmic ovules, probably due to an elimination of the outer integument. Likewise, the lack of the testa (i.e., developed outer integument), the "endotegmic" seed coat, and the perichalazal seed at maturity are also characteristics of Siparunaceae. Within the family, Siparuna differs from Glossocalyx in having plural tetrads of megaspores and plural, starchy-rich, one-nucleate, tubular embryo sacs (autapomorphies). On the other hand, Glossocalyx is characterized by having bilaterally flattened seeds (autapomorphy). Although functional aspects of those autapomorphies are uncertain, both Glossocalyx and Siparuna show evolution in different embryological characters.

Comparative Gynoecium Structure and Development in Calycanthaceae (Laurales)

“…In all taxa studied, the ovule vascular bundle appears to branch into four small bundles that extend into the base of the outer integument ( fig. 12), as previously reported in young seeds of Calycanthus and Chimonanthus (Corner 1976) and anthetic ovules of Idiospermum ; reviewed by Kimoto and Tobe 2001). In the upper (sterile) ovule, the time of onset of abortion is variable even at the species level.…”

“…However, a few character states present in Calycanthaceae are shared by most of the order: ovules anatropous (with the exception of Gomortega, orthotropous; Endress and Igersheim 1997;Heo et al 2004), bitegmic (except for Siparunaceae, unitegmic;Heilborn 1931;Endress 1972;Renner et al 1997;Kimoto and Tobe 2003), and crassinucellar . The outer or the only integument is semiannular or annular, with both character states observed in the same species in Peumus of Monimiaceae and Siparuna of Siparunaceae .…”

Ancestral traits and specializations in the flowers of the basal grade of living angiosperms

“…(Lauraceae; Endress & Igersheim, 1997a;Heo & al., 1998), and Siparuna Aubl. (Siparunaceae;Endress, 1972;Kimoto & Tobe, 2003).…”

Embryology of Gomortegaceae (Laurales): characteristics and character evolution

“…Serial resin sections cut to a thickness of 4-6 mm were stained with 0.5% toluidine blue for 10 s or with Heidenhain's hematoxylin. To examine vasculature and inserted positions of integuments (a testa and tegmen), a few ovules and young seeds were bleached with sodium hypochlorite (NaOCl) at room temperature for 12-24 h. After being washed several times with water, they were dehydrated through an ethanol series, cleared with Herr's 41/2 clearing fluid, and observed on Raji slides (Herr 1974;Kimoto and Tobe 2003). To count the generative cells in mature pollen, mature pollen grains were stained with 1% acetocarmine.…”

“…Sections cut to a thickness of 5-8 mm were stained with Heidenhain's hematoxylin, safranin O, and fastgreen FCF, and mounted with Entellan (Merck, Germany). To examine fine structure, a few flower buds and fruits were embedded in Technovit 7,100 (Kulzer, Wehrheim, Germany), after dehydration through an ethanol series (Kimoto and Tobe 2003). Serial resin sections cut to a thickness of 4-6 mm were stained with 0.5% toluidine blue for 10 s or with Heidenhain's hematoxylin.…”