Abstract Detail

Paleobotany

Pipo, M Laura [1], Bodnar, Josefina [2], Iglesias, Ari [3].

A vessel-less stem with cambial variants from the Late Cretaceous of Antarctica.

Cambial variants (cambium activity that differs from that of the typical bifacial cambium) are registered since the Paleozoic in many different plant groups. Although in the past this type of growth was present in self-supporting gymnosperms, nowadays is predominant in angiosperm lianas. In this contribution we describe the first macrofossil record of a vessel-less stem with cambial variants preserved in calcareous concretions from Campanian (Late Cretaceous) sediments in the James Ross Island, Antarctic Peninsula, and discuss its assignation among Chlorantaceae. The stem is circular and 5 mm of diameter in traverse section. It has a wide pith with large isodiametric parenchyma cells. The primary vascular system is formed by one cycle of collateral vascular bundles, with endarch protoxylem. The secondary vascular cylinder is radially dissected, with segments of axial xylem and phloem alternating with large interfascicular rays produced by differential cambial activity (cambial variant). These rays are multiseriate (up to 8 cells wide) homocellular and homogeneous consisting of square parenchyma cells. The xylem wedges contain tracheids and uniseriate homocellular and homogenous rays. Growth rings are indistinct and axial parenchyma is absent. With respect to the secondary phloem, the phloematic fibers are arranged in caps. Sieve cells were not identified. The bark is composed by dead cells of secondary phloem and cork cells which are accumulated in a multilayered rhytidome. Although the studied fossil share the absence of vessels and the wide rays with some gymnosperms (e.g. seed ferns and cycads), those rays are different in composition in comparison with seed ferns or different in origin in comparison with cycads. The anatomical features (vessel-less, wide interfascicular rays) allow us to relate the fossil stem to extant Sarcandra, a rare genus within Chloranthaceae. Studies of Sarcandra stem anatomy do not mention the activity of a cambial variant, but emphasize that the wide rays are a product of the interfascicular cambium. We consider this kind of pattern as a type of cambial variant since the interfascicular cambium does not produce the same cells than the fascicular one. The Antarctic specimen shows small differences with Sarcandra, indistinct growth rings, square ray cells and complete absence of vessels, as a consequence we proposed that the studied fossil belong to a new taxon. The new Antarctic taxon may have an ecological habit similar to shrub-like Sarchandra species, representing the discovery of a new forest structure element in the Cretaceous floras.

1 - INIBIOMA, Quintral 1250, Bariloche, 8400, Argentina
2 - La Plata National University , Paseo del bosque s/n, La Plata, Buenos Aires, 1900, Argentina
3 - INIBIOMA, Quintral 1250, Bariloche, Rio Negro, 8400, Argentina

Keywords:
Chloranthaceae
Sarcandra
stem anatomy
wood
cambial variants
Cretaceous
Antarctica
Gondwana.

Presentation Type: Oral Paper
Session: 28, Cookson Award Session I
Location: 109/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 2:30 PM
Number: 28005
Abstract ID:186
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award