Spirodela SCHLEID.

Smith, MacKenzie A., Greenwalt, Dale E. & Manchester, Steven R., 2023, Diverse Fruits And Seeds Of The Mid-Eocene Kishenehn Formation, Northwestern Montana, Usa, And Their Implications For Biogeography, Fossil Imprint 79 (1), pp. 37-88 : 49

Genus Spirodela SCHLEID.

Text-fig. 4a–d

M a t e r i a l. USNM PAL 624518, 625611, 768304.

L o c a l i t i e s. Dakin and Spring.

D e s c r i p t i o n. Plants with elliptical fronds 1.1– 3.9 mm long, 1.5–2.5 mm wide; prophylla present, 0.8– 1.1 mm long, 1.1–1.4 mm wide; brown pigment cells present.

The presence of large prophylla and brown pigment cells places these plants within Spirodela ( Armstrong 2021) . Prophylla are absent in Lemna L. and reduced in Landoltia LES et D.J. CRAWFORD ( Armstrong 2021) . We interpret the brown, circular dots that are concentrated near the prophylla and more dispersed in the distal portion of the leaves as brown pigment cells. Brown pigment cells are absent in Lemna but present in Spirodela ( Armstrong 2021) . Spirodela was described from the Paleocene of Alberta and Saskatchewan ( Dawson 1875, Berry 1935, McIver and Basinger 1993) and the middle Eocene of Wyoming ( MacGinitie 1974), but these fossils were subsequently transferred to the extinct araceous genus Limnobiophyllum KRASSILOV ( Kvaček 1995, Stockey et al. 1997).

Figures

Text-fig. 4. Lemnoideae from the Kishenehn Formation. a: USNM PAL 625611 Spirodela sp. showing fronds, prophyllum and daughter plant with brown pigment cells. Scale bar 2mm. b: Close up of USNM PAL 625611 prophyllum and brown pigment cells. Scale bar 1mm. c: USNM PAL 768304 Spirodela sp. showing fronds, prophyllum and daughter plant with brown pigment cells. Scale bar 2.5mm. d: Close up of USNM PAL 768304 daughter plant with brown pigment cells. Scale bar 2.5mm. e: USNM PAL 620300 Lemna sp. showing fronds with aerenchyma and pseudoroot. Scale bar 1mm. f: USNM PAL 626140 Wolffiella sp. “tongueshaped” multicellular frond with brood pouch at the base. Scale bar 2mm. g: Modern Wolffiella caudata frond with brood pouch and daughter plant from Pagliuso et al. 2018. Scale bar 1 mm.