Anogeissus sp.

Sakala, Jakub, 2000, Silicified angiosperm wood from the Dangu locality (Ypresian of the Gisors region, Eure, France) - final part: the problem of palaeoclimate reconstruction based on fossil wood, Geodiversitas 22 (4), pp. 493-507 : 498-500

Anogeissus sp. ( Figs 4 ; 5B, D, E )

DESCRIPTION

The growth rings are slightly distinct due to the presence of terminal parenchyma.

The wood is diffuse porous.

The vessels are solitary (15%) or in radial (rarely in tangential) multiples of 2 (25%), 3 (20%), 4 (15%), 5 to 10 (20%) or more than 10 (up to 21) (5%), in number of 25 vessels (100 pores) per

PT

mm 2. The tangential diameter varies from 22 to 91 µm (mean 57 µm), the radial diameter varies from 22 to 109 µm. The vessel elements, from 85 to 445 µm (mean 180 µm) in length, have subhorizontal simple perforation plates. The walls of the pores are 3-8.5 µm thick. The intervascular pits are bordered, alternate, non-vestured, very dense and 1.5-3 µm in diameter.

The fibres are arranged in one to 15 radial, rather regular, series between the rays. They are at least 640 µm long and are sometimes septate. The tangential diameter reaches 14 µm, the wall thickness is about 4.5 µm. The pits are not visible. The axial parenchyma is in three to five cells thick tangential bands and terminal. The cell dimensions (tangential diameter × radial diameter × height) are 6-18 µm × 3-21 µm × 58- 85 µm. The cells have dark contents.

The rays are uniseriate or rarely biseriate in one to eight cells tall portions, heterogeneous (type 7 of Metcalfe & Chalk 1989: 23), 18-24 in number per horizontal tangential mm. They are 11-37 µm wide and 3-30 cells (100-930 µm) high. In the tangential section, the cell dimensions (height × width) are 44-64 µm × 12-23 µm. Examples of radial dimensions (height × length) of the different types of cells are: upright cells 44 × 21; 64 × 22... µm, square cells 29 × 32... µm and procumbent cells 29 × 66; 32 × 131... µm.

DISCUSSION

The studied wood, with its bands of terminal parenchyma and vessels in frequent radial multiples, shows affinities with some genera of the families Meliaceae , Rutaceae , Sapindaceae , Sapotaceae , Apocynaceae and Combretaceae .

Among these six families, there is no species that corresponds in all features to the fossil wood (Heimsch 1942; Metcalfe & Chalk 1950). The Sapotaceae family is the closest in general vessel arrangement, although unlike the fossil at hand, its representatives show regularly banded parenchyma and no septate fibres, when uni- (or rarely biseriate) rays are present. In Combretaceae , Anogeissus and Lumnitzera have vessels in radial multiples and uniseriate (rarely biseriate) rays (Metcalfe & Chalk 1950). Furthermore, some species of Anogeissus have septate fibres (Metcalfe & Chalk 1950). The absence of terminal parenchyma in the extant Anogeissus has probably no systematic importance; its presence in the fossil wood may be due to environmental conditions. This problem is discussed below (see below “Sedimentation pattern and climatic conditions based on wood anatomy observations”).

The fossil is identified only to the genus. Because our wood does not fit the diagnosis of the fossil genus Anogeissuxylon (Louvet 1965: 295-296) and no other similar wood plan has been found in the fossil record, the living genus Anogeissus is proposed. Its characteristic of wood fits the Dangu fossil very well. The absence of terminal parenchyma in Anogeissus is not considered to be of systematic importance.

Figures

FIG. 4. — Anogeissus sp. (W4), cross-section. Abbreviations: F, fibres; PBT, parenchyma in tangential band; PT, terminal parenchyma; R, rays; V, vessels. Scale bar: 200 µm.

FIG. 5. — A, Dichrostachyoxylon cf. zirkelii (SY7), cross-section; B, Anogeissus sp. (W4), cross-section; C, Dichrostachyoxylon cf. zirkelii (SY7), tangential section; D, Anogeissus sp. (W4), tangential section, detail of a septate fibre (septum indicated by the arrow); E, Anogeissus sp. (W4), tangential section, general view. Scale bars: A, B, 500 µm; C, 100 µm; D, 50 µm; E, 200 µm.