Mesocyparis borealis MCIVER et BASINGER

Manchester, Steven R., 2014, Revisions To Roland Brown’S North American Paleocene Flora, Acta Musei Nationalis Pragae Series B 70 (3 - 4), pp. 153-210 : 158-159

Mesocyparis borealis MCIVER et BASINGER

Foliar branches referred to Thuja interrupta NEWBERRY by Brown (1962) have been revised multiple times. Hickey (1977) called this species Thuites interruptus (NEWBERRY) BELL , using Sternberg’s genus Thuites . McIver and Basinger (1987) placed them in Cupressinocladus interruptus (NEWBERRY) SCHWEITZER , adopting Schweitzer’s (1974) recommendation that the form-genus Cupressinocladus Seward be applied to vegetative material when reproductive organs are not present. The same kind of foliage, with attached cones, was placed in a new genus and species, Mesocyparis borealis , from the Paleocene of Ravenscrag, Saskatchewan ( McIver and Basinger 1987). A short time later, Golovneva (1988) published a similar new genus and species as Microconium beringianum . In their subsequent survey of Cretaceous and Tertiary Thuja -like remains, McIver and Basinger (1989, p. 1911) considered oppositely branching foliage as Chamaecyparis interruptus (NEWBERRY) SCHWEITZER , but it seems likely that these represent fragments of Mesocyparis . Under the philosophy that vegetative and reproductive branches be treated separately, the appropriate names for this taxon are Cupressinocladus interruptus (NEWBERRY) SCHWEITZER , and (if cones are attached) Mesocyparis borealis MCIVER et BASINGER. The reason for this is that the same kind of foliage could be produced by more than one genus of Cupressaceae , and is thus placed in a catchall fossil-genus. The presence of cones permits a better resolved identification.

Angiosperms

Nymphaeaceae

Brown included Cabomba inermis (NEWBERRY) HOLLICK , Nymphaea leei (KNOWLTON) R. W. BROWN , Nymphaea pulchella (KNOWLTON) R. W. BROWN , and Paleonuphar hesperium R. W. BROWN among the water lilies cited from the Paleocene floras. The leaves assigned to Nyphaea appear to be correctly identified. The remains assigned to Cabomba are dichotomously branched unwebbed structures that correspond closely to roots known for the non-nymphaealean extinct genus, Quereuxia . The extinct genus Paranymphaea was subsequently transferred to Polygonaceae by McIver and Basinger (1993; see below).

Magnoliaceae

“ Bauhinia” wyomingana R. W. BROWN. Although bilobed with a laminar outline similar to that of Bauhinia , the illustrated specimen differs in venation (pinnate, rather than actinodromous) and lacks the petiole morphology expected for that genus, and other legumes. It appears, instead to represent a leaf of Magnoliaceae , cf. Liriodendron . It is closely similar to the leaf known as Liriodendron iijimae TANAI from the upper Cretaceous (Senonian) of Japan ( Tanai 1979). Kirk Johnson (1996, in his discussion of another taxon, Liriodendrites bradacii K. JOHNSON) mentioned that more specimens of this kind occur in the Great Divide Basin. “ B.” wyomingiana is represented only by the single specimen illustrated by Brown, and the upper fragment is missing from the type collection, so that only the basal part of the illustrated specimen is available for continued study. The original site for this species is no longer accessible due to completed mining activity.

Although Brown (1962) treated several species as Magnolia , the leaf architectural characters of extant Magnolia are not unique to that genus or family. Entire-margined pinnately veined leaves occur in many families so the assignment of Magnolia is based on general similarity rather than on diagnostic characters.

Lauraceae

Leaves of Lauraceae are entire-margined with pinnate secondaries that in some genera can be arranged with a basal or suprabasal pair of acrodromous secondaries. Similar venation can occur elsewhere among angiosperms, for example in Araliaceae , Hamamelidaceae , and Menispermaceae . When cuticle is preserved documenting paracytic stomata and oil cells, the affinities with Lauraceae can be substantiated, but cuticle was not examined for the species investigated by Brown. The familial and generic assignments for these taxa need verification: Cinnamomum sezannense WATELET , Laurophyllum caudatum (KNOWLTON) R. W. BROWN ; Laurophyllum perseanum R. W. BROWN ; Laurus socialis LESQUEREUX ; Lindera obtusata (WARD) R. W. BROWN ; Persea brossiana LESQUEREUX ; and Sassafras thermale (LESQUEREUX) R. W. BROWN.

“ Melastomites” montanensis R. W. BROWN. Brown (1962) noted that the leaves he attributed to Melastomites Unger are similar to those of Sassafras and Cinnamomum ( Lauraceae ) as well as with Tococa of Melastomataceae . The leaves do not, however, show the strongly impressed percurrent tertiaries typical of Tococa and other Melastomataceae . Brown indicated that “surfaces of the better preserved leaves display minute dots, about 300 per sq cm, that were probably glandular”. These might represent the hardened contents of oil cells common in Lauraceae .

“ Artocarpus” lessigiana (LESQUEREUX) KNOWLTON. Brown (1962) provided a helpful synonymy of the previously published occurrences of this species. The leaves are large, and deeply pinnately lobed with deep, rounded intralobal sinuses, superficially resembling extant Artocarpus . Kirk Johnson (pers. comm. 2014) noted: “We dug hundreds of “ Artocarpus ” leaqves in the Denver Basin, most from the first 2–3 million years of the Paleocene. They could be quite large, up to 20 inches long so they continue the resemblance to Artocarpus , but lack all of the distinctive venation of Moraceae . At Castle Rock, we also collected leaves that were strikingly similar to true Sassafras in their morphology and venation. Close comparison of the big lobed “ Arctocarpus ” with the Sassafras suggested affinity to the Lauraceae .” Garland Upchurch studied the cuticles of similar specimens from the Denver and Raton Basin and also indicated lauralean affinities (Kaufmann et al. 1990; Upchurch and Wolfe 1987).

Chloranthaceae