Notes on Fossil Leaves

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Introduction

Fossil material of plants can be difficult to identify as to species, genus, or larger taxonomic units, as usually what is found is individual parts of plants, such as wood, leaves, flowers, fruits, seeds or pollen, and these are often insufficient for identification, particularly for older material why is less closely related to modern material, and may be less well preserved. Consequently, and as fossils of one plant part often cannot be unambigiously associated with those of another plant part, palaeobotanists use form genera to classify parts of plants of uncertain taxonomic position. The suffix -phyllum is often used in generic names, indicating a similarity with the leaves of the modern genus whose name is combined with that suffix. It cannot be assumed that the fossil leaves represent a species particularly close to the modern genus.

I suspect that the genera and species of fossil malvaceous leaves listed below are far from an exhaustive coverage. Furthermore fossil leaves may be ascribed to a living genus, and this will be even harder to track down.

The identification of fossil leaves is particularly difficult, and historically many errors have been made. Early identifications were often made on the basis of the overall shape of the leaf, which is not a reliable guide. (A great many leaf fossils, including some now though to be malvaceous, were originally identified as Ficus.) More modern work takes account of the details of the venation, the architecture of the stomata, and the nature of the indumentum. However as even living plants can be difficult to identify in the absence of flowers or fruits I retain some skepticism.

Actinovena

Actinovena Tanai is a genus introduced for leaves believed to be tiliaceous (perhaps related to Pentace). These leaves are nearly symmetrical, ovate to narrowly ovate, 3-nerved and rounded at the base, with entire margins and acuminate apices. The assignment to Tiliaceae is based on details of the secondary and subsequent venation.

The name refers to the actinodromous nature of the primary venation.

Actinovena ishikariensis Tanai is recorded in the Late Eocene Ikushunbetsu Fm of Hokkaido. [2]

Bombacites

Leaf fossils described as Bombacites jacksoniana are recorded from Eocene (Jackson Fm.) of Texas.

Bombacites ceibaoides Ball is recorded from the Eocene (Wilcox Fm.) of Texas and Bombacites formosus Berry from the Eocene (Wilcox Fm.) of Louisiana and Texas

Bombacites orientalis Lakhanpal is recorded from the Upper Palaeocene (Tura Fm.) of Assam and Meghalaya.

Bombaciphyllum

Bombaciphyllum is a form genus representing fossil leaves similar to those of the genus Bombax (or bombacoids in general). However fossil leaves perceived to similar to living Bombax are more commonly placed in that genus, than in Bombaciphyllum.

Bombaciphyllum argillaceum is recorded from the Upper Cretaceous. It may well be the same as Bombax argillaceum. Bombaciphyllum opacum Engelhardt is recorded from the Tertiary of Chile.

Bombax

Leaves (leaflets) assigned to Bombax sturtii Ettingshausen and Bombax mitchellii Ettingshausen are recorded from the Tertiary of Australia. Leaves assigned to Bombax chorisioides Friedr. and Bombax lepsii Engelhardt are recorded from the Lower Tertiary of Germany

Brachychiton

Leaf material ascribed to Brachychiton is reported from the Tertiary of Australia and New Zealand. Brachychiton-like leaves have also been found in South America.

Byttneriophyllum [e]

Byttneriophyllum is a form genus representing fossil leaves similar to those of the genus Byttneria.

Byttneriophyllum tiliaeofolium is recorded from the Neogene of Slovenia, the Miocene of Poland, the Middle Miocene of Romania, and also from East Asia. It has been confused with Dombeyopsis lobata, from which it differs in possessing a strongly asymetrical leaf base. Whether this represents a malvaceous plant is not clear; on the one hand it is associated with the malpighiaceous fruit morphospecies Banisteriaecarpum giganteum, on the other hand it has been associated with the pollen morphospecies Intratriporopollenites instructus, which is probably tilioid.

Byttneria iizimae Tanai is recorded from the Late Eocene Ikushunbetsu Fm of Hokkaido. It is similar to Byttneriophyllum tiliaeophyllum, from which it differs in its more nearly symmetric base, and in its sparser tertiary venation. [2]

Buettneria blackiiBall is recorded from Eocene (Wilcox Fm.) of Texas, and Buettneria jacksoniana Berry from the Eocene (Jackson Fm.) of Texas. Buettneria asterotrichiformis and Buettneria lanceolatifolia are recorded from the Eocene or Miocene of Argentina. (Buettneria is a variant spelling of Byttneria.)

Byttneriopsis

[4]

Cola

Leaf material ascribed to Cola, under the name Cola amharensis, is recorded from the Late Oligocene of northwestern Ethiopia.

Empedoclea

Empedoclea is a living genus, belonging to Dilleniaceae. However, the fossil Empedoclea repando-serrata Engelhardt, from Chile, is believed to be bombaceous, and perhaps to be placed in Bombax.

Fremontodendron

Leaf material assigned to "Fremontia" coriacea and "Fremontia" lobata is found in the Miocene of California. Material referred to the former is also found in the Pliocene (Piru Gorge), and to the latter in the Miocene Kinnick and Pliocene Tasssajero Fms. Material referred to "Fremontia" is also found in Eocene deposits in Yellowstone.

Grewia

Fossil leaves from the Tertiary of North America and Eurasia (including Greenland and Spitzbergen) have in the past been assigned to various species of Grewia, including Grewia auriculata, Grewia crenata, Grewia crenulata and Grewia obovata; these four species are now all assigned to Trochodendroides crenulata (Cercidiphyllaceae). These should not be confused with living Grewia species with the same names.

Grewia mallotophylla is recorded from the Miocene of Nepal [b]. (This is one of several species described in a paper based on leaf and seed macrofossils; the abstract doesn't indicate on which G. mallotophylla was raised, but the specific name is a strong hint that it is based on leaf material.) Grewia tiliaefolia and Grewia tistaensis are recorded from the Middle Miocene of West Bengal [a].

Other material assigned to Grewia includes

Kleinhovia

Leaves assigned to the species Kleinhovia basitruncata (Oishi & Huzioka) Tanai are recorded from the Late Eocene Ikushunbetsu Fm of Hokkaido. These were previously assigned to Marlea basitruncata Oishi & Huzioka and Alangium basitruncatum (Oishi & Huzioka) Tanai.

They differ from the leaves of the sole living species, Kleinhovia hospita, in being truncate to broadly rounded at the base (rather than cordate). [2]

Luehea

Luehea roxoii Dolianiti is described from a leaf fossil from the Pliocene of Minas Gerais in Brasil.

Material assigned to Luehea newberryana (Knowlton) is found in the Early and Middle Eocene of Wyoming. This is now considered to belong to Populus [d].

Malvaciphyllum

Malvaciphyllum is a form genus representing fossil leaves similar to those of living mallows.

Malvaciphyllum quenquiadensis is recorded from the Upper Miocene of Argentina, and fossils assigned to this genus, but to no specific species, from the Pliocene of Brasil [f]. The former is thought to be related to Abutilon [3].

Plafkeria

Plafkeria includes leaf fossils from the Palaeogene of North America and North East Asia, and is considered to be tiliaceous. They were originally named as Willisia, but this turned out to be a junior homonym of a genus in Podostemonaceae, and Plafkeria was introduced as a replacement name. They have asymmetric leaf blades and palmate venation.

Plafkeria obliquifolia is reported from the Late Oligocene of Oregon and the Eocene of California.

Plafkeria basiobliqua (Oishi & Huzioka) Tanai is reported from the Late Eocene Ikushunbetsu Fm of Hokkaido. Other names for this taxon include Marlea basiobliqua Oishi & Huzioka, Alangium basiobliquum (Oishi & Huzioka) Tanai, Ficus ezoensis Endo, Ficus planicosta Endo and Ficus platanifolioides Endo. Specimens of this taxon have also been assigned to Ficus tiliaefolia (Braun) auct. non Heer and Ficus yubariensis Endo. [2]

Plafkeria rentonensis

Plafkeria, unspecified as to species, is recorded from the Lower Eocene of British Columbia, and from the Eocene Kushutaka Fm of Alaska [2]. The latter may represent Plafkeria basiobliqua.

Protophyllum

Pterygota

Pterygota ezoana Tanai is recorded from the Late Eocene Ikushunbetsu Fm of Hokkaido. These leaves are similar to those of the living Pterygota alata, but differ in being broadly rounded to broadly cordate (as opposed to usuallly broadly cordate), and in finer venation. [2]

Sphaeralcea

Sphaeralcea exhumata is recorded (as Malvastrum exhumatum Cockerell) from the Florissant Fm of Colorado. An image of a leaf is available at the Florissant Fossil Beds National Monument web site.

Sterculia

Leaf fossils assigned to Sterculia are found in the Eocene to Oligocene of Europe, and in other areas of the world. A palmate lobed form from Dalmatia and Slovenia is known as Sterculia labrusca.

Tiliaephyllum

Tiliaephyllum is a form genus representing fossil leaves similar to those of the genus Tilia. As this form genus is recorded from the Upper Cretaceous, and the fossil record of Tilia otherwise extends no earlier than the Palaeocene, it seems to me that these leaves do not belong to Tilia, and may not belong to Malvaceae. (Confusion between fossil TIlia and Populus (Salicaceae) leaves, for example, has occurred.) In particular Tillaephyllum dubium Newberry from the Turonian Raritan Fm is too early to be malvaceous.

Tiliaephyllum tsagajanicum is recorded from Manchuria, Kamchatka, the Amur river region, and northern Alaska. It may be referable to Davidia [c].

References

  1. Kvacek, Z., Early Miocene records of Craigia (Malvaceae s.l.) in the Most Basin, North Bohemia - whole plant approach, Journal of the Czech Geological Society 49(3/4): 161-171 (2004)
  2. Tanai, The Revision of the so-called "Alangium" Leaves from the Paleogene of Hokkaido, Japan, Bull. Natn. Sci. Mus., Tokyo, Ser. C 15(4): 121-149 (1989)
  3. Anzótegui, L., & Herbst, R., Megaflora (hojas y frutos) de la Formación San José (Mioceno Medio) en Río Seco, Departamento Santa María, provincia de Catamarca, Argentina
  4. Kvacek, Z. & Wilde, V., Foliage and seeds of Malvalean plants from the Eocene of Europe, Bulletin of Geosciences 85(1): 103–122 (2010)

Bibliography

  1. J. S. Antal and M. Prasad, Morphotaxonomic study of some more fossil leaves from the lower Siwalik sediments of West Bengal, India, The Palaeobotanist 47: 88-98 (1998)
  2. Konomatsu & Awasthi, Plant fossils from Arung Khola and Binai Khola formations of Churia Group (Siwalik), west central Nepal, and their palaeoecological and phytogeographical significance. The Palaeobotanist 48(2): 163-181 (1999)
  3. Manchester, S.R., Leaves and Fruits of Davidia (Cornales) from the Paleocene of North America, Systematic Botany 27(2): 368-382
  4. Manchester, S.R. et al, Foliage and Fruits of Early Poplars (Salicaceae: Populus) from the Eocene of Utah, Colorado, and Wyoming, International Journal of Plant Sciences 167: 897-908 (2006)
  5. Givulesco, R., Observations nouvelles sur Byttneriophyllum tiliaefolium (al. Braun) Knobloch et Kvacek, Review of Palaeobotany and Palynology 10(3): 233-242 (1970)
  6. Anzótegui, L., & Cristalli, P., Primer registro de hojas de Malvaceae en el Neogeno de Argentina y Brasil, Ameghiniana 37(2): 169-180 (2000)

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