Callicrypta chlamydea, Krassilov & Golovneva, 2004

Krassilov, Valentin A. & Golovneva, Lena B., 2004, A minute mid-Cretaceous flower from Siberia and implications for the problem of basal angiosperms, Geodiversitas 26 (1), pp. 5-15 : 10-14

Callicrypta chlamydea n. sp. ( Figs 1-3 )

HOLOTYPE. — Komarov Botanical Institute, St. Petersburg, No. 1181-3-585(1), a flower from the Cenomanian (Timerdyakhskaya Formation) of the middle reaches of Tyung River about 200 km upstream of its confluence with the Vilyuy River , eastern Siberia.

ETYMOLOGY. — Chlamidea (from Greek) with a mantle (perianth).

DIAGNOSIS. — As for the genus.

DISCUSSION

Callicrypta chlamydea n. gen., n. sp. is similar to Amborellaceae in general aspect of the minute diclinous oligomerous flowers of free parts, with one or few staminodes and with a single whorl of five or six gibbose ascidiform carpels. At the same time, it shares with the Menispermaceae and/or the allied ranunculid families Sargentodoxaceae , Lardizabalaceae and Kingdoniaceae such diagnostic features of floral morphology as the calyx of petaloid sepals, corolla of more numerous biseriate nectariferous petals which are smaller than sepals, imbricate and valvate, clasping the staminodes, and the apocarpous gynoecium of six carpels with a short style. Callicrypta chlamydea n. gen., n. sp., thus, indicates an affinity between the Amborellaceae and Menispermaceae , which can be reinforced by involving in the comparison the staminate flowers of the Cretaceous ranunculid Freyantha sibirica which produced pollen of the same type as found attached to Callicrypta chlamydea n. gen., n. sp.

The morphological comparison ( Table 1) places both these Cretaceous species in the plexus of archaic ranunculids the present day survivors of which form the monotypic families Sargentodoxaceae , Kingdoniaceae , Circaeasteraceae , Glaucidiaceae and the closely allied Amborellaceae . A traditional assignment of Amborella to the Laurales (Monimiaceae) is based mainly on a single feature in common, the inflated floral receptacle ( Cronquist 1981) that occurs, although in a less conspicuous form, in the Menispermaceae also. A recently advocated link to the Nymphaeales ( Mathews & Donoghue 1999; Qiu et al. 1999), an order of aquatic angiosperms, is scarcely justified by a few homoplastic features in common, such as the porose vessels ( Schneider & Carlquist 1996) or a spiral floral phyllotaxis, widely scattered among the angiosperm orders. The tracheary elements in Amborella with small pores in pit membranes or altogether lacking pit membranes are unlike those in Nymphaeaceae with large pores ( Field et al. 2000). The more strictly diagnostic features of the flower topology, gynoecium, ovules, fruit, pollen grains, etc., are so disparate that a detailed comparison does not make much sense. Basic nymphaeaceous floral structure has been fairly distinct in the mid- Cretaceous already ( Krassilov & Bacchia 2000).

We emphasize the extreme diminution of the flower in Callicrypta n. gen. not only because it counters once popular idea of primitiveness, but also because dimensions are important in pollination ecology. Our studies of gut contents of fossil insects have revealed a widespread Palaeozoic and Mesozoic pollen feeding by various relatively large insects, such as hypoperlids, booklice, katydids and xyelids ( Krassilov & Rasnitsyn 1998). Floral organs of proangiosperms might have been visited for pollen primarily, as in the case of Preflosella , an Early Cretaceous pre-flower foraged by two xyelid species ( Krassilov & Rasnitsyn 1998). Co-adaptation of plants and pollinivorous insects implied a certain robustness of floral organs.

A miniaturization of floral parts accompanied by a development of secreting structures (glands on the bracteate tepals in Freyantha sibirica and on the inner petals in Callicrypta chlamidea n. gen., n. sp.) suggests a major innovation in pollination ecology involving new groups of insects coming for nectar and capable of gently handling the flower. This line of co-evolution might have led to a diversification of forms related to the present-day ranunculids. The finds of such forms in the mid-Cretaceous of Siberia and northern Kazakhstan ( Caspiocarpus: Vakhrameev & Krassilov 1979 ; Krassilov 1984; Hyrcantha: Krassilov et al. 1983 ) suggest a diversification center in the northern temperate realm.

Figures

FIG. 1. — Callicrypta chlamydea n. gen., n. sp. from the Cenomanian of Vilyuy Basin, Siberia, SEM photographs; A, holotype, a pistillate flower with a calyx, biseriate corolla, and apocarpous gynoecium (see Fig. 2 for interpretation); B, carpel with a short style, abaxial aspect; C, radial sequence of sepal (S), outer petal (Po), inner petal (Pi) and carpel (C), the carpel is split in the median plane showing the locule, the position of papillate gland on the inner petal is marked as n; D, tubular structure (staminode?) clasped at base by the inner petal; E, papillate gland (nectary?) below the apical notch of an inner petal (see n); F, carpel, lateral view, style missing. Scale bars: A, 300 µm; B, 120 µm; C, 90 µm; D, 40 µm; E, 21 µm; F, 70 µm.

FIG. 2. — Callicrypta chlamydea n. gen., n. sp., a flower from the Cenomanian of Vilyuy Basin, Siberia, outline of the holotype (see Fig. 1A) showing interpretation of the floral parts. Abbreviations: C, carpel; Pi, inner petal;Po, outer petal; S, sepal; St, staminode?. Scale bar: 150 µm.

FIG. 3. — Pollen grains adhering to the petals and carpels of Callicrypta n. gen., n. sp., a pistillate flower from the Cenomanian of Vilyuy Basin, Siberia; A, polar aspect; B, oblique equatoriopolar aspect; C, lateral aspect. Scale bars: 3 µm.