The Fossil Record of Basal Monocots

Abstract

The fossil record of basal monocots (Acorales and Alismatales) extends back to the Cretaceous in the Northern Hemisphere. While many fossils were originally assigned to these basal groups, rigorous paleobotanical studies show many of them to be misidentified. Acarus fossils have been reliably reported from the Eocene while those of Alismatales extend back to the early Cretaceous. The fossil record of basal monocots is usually represented by leaves, fruits, and seeds; however, some localities preserve stems with attached leaves and roots and even whole plants. A detailed examination of leaf venation patterns in alismatids has recently allowed the description of a new taxon from the Upper Cretaceous of Alberta based on leaves attributed to Limnocharitaceae. Anatomically preserved alismatid petioles (Heleophyton helobiaeoides) and well-preserved flowers/fruits are known from the Middle Eocene Princeton chert of British Columbia. A complete developmental sequence from flower to fruit is known, and this material has good possibilities for whole plant reconstruction. The extinct floating aquatic Limnobiophyllum (Araceae!Lemnoideae) and the genus Pistia have been the subject of morphological cladistic analyses and competing hypotheses of relationships among aroids and duckweeds. The fossil record and recent molecular studies support separate origins of Pistia and the duckweeds from within Araceae. The fossil taxon "Pistia" corrugata has been reexamined in light of new evidence and indicates the presence of a new genus that shows leaf morphology unlike that seen in extant Pistia, but with a similar growth habit. Fossil evidence indicates that the floating aquatic habit probably arose at least three times within Araceae.

The age of major monocot groups inferred from 800+rbcL sequences

“…Using eight reference fossils, Bremer (2000) estimated the age of the split between Acorus and all other monocot lineages at 134 Mya. Later, it has been shown that one of Bremer's reference fossils (fossil B) is not a Pistia of Araceae as assumed, but a different, unknown plant (Stockey, 2003). Recalculation of the mean change rates used by Bremer, and recalibration without that fossil gives, however, the same result.…”

Establishing a fossil record for the perianthless Piperales: Saururus tuckerae sp. nov. (Saururaceae) from the Middle Eocene Princeton Chert

“…DISCUSSION-Affinities of the fossil flowers-These fossil flowers have previously been thought to represent an undescribed alismatid taxon (Currah and Stockey, 1991;Stockey, 1994Stockey, , 2001Pigg and Stockey, 1996;Stockey, 2004, 2005). Morphologically, the fossil flowers resemble some families of Alismatales (particularly Aponogetonaceae, Juncaginaceae, and Potamogetonaceae) and Piperales (Saururaceae), all of which have minute flowers borne on spikes (or racemes).…”

“…No fossil vegetative or pollen remains have been firmly placed in the family Saururaceae. However, we recently recognized that fossil flowers from the Middle Eocene Princeton Chert, previously thought to have affinities to Alismatales (Currah and Stockey, 1991;Stockey, 1994Stockey, , 2001Pigg and Stockey, 1996;Stockey, 2004, 2005), have many similarities to saururaceous flowers. Here, we describe this flower type and demonstrate that while these fossil flowers are similar to certain alismatids, floral and inflorescence structure and anther contents suggest that this flower type is related to Saururaceae (Piperales).…”

A review of the plants of the Princeton chert (Eocene, British Columbia, Canada)

“…The evolution of the monocots have been a topic of considerable interest in recent years, and several authors have looked to the fossil record for information about the evolution and phylogeny of this group (e.g., Stockey 2006;Smith 2013). Among the most noteworthy contributions of the Princeton chert plants are several reports of anatomically preserved monocots.…”