Botany

Fossil species of Boehmerieae Gaudich. (Urticaceae) in Dominican and Mexican : A new genus (Ekrixanthera) and two new species with anemophilous pollination by explosive pollen release, and possible lepidopteran herbivory

Journal: Botany

Manuscript ID cjb-2016-0006.R2

Manuscript Type: Article Date Submitted by the Author: 04-May-2016Draft Complete List of Authors: Poinar, Jr., George; Oregon State University, Department of Integrative Biology Kevan, Peter; Environmental Biology Jackes, Betsy; James Cook University

palaeobotany, anemophily, Ekrixanthera hispaniolae, Ekrixanthera ehecatli, Keyword: paleoecology

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Fossil species in Boehmerieae Gaudich. (Urticaceae) in Dominican

and Mexican amber: A new genus ( Ekrixanthera ) and two new

species with anemophilous pollination by explosive pollen release,

and possible lepidopteran herbivory

GEORGE POINAR, JR. 1 PETER G. KEVAN 2 AND BETSY R. JACKES 3

1Department of Integrative Biology, Oregon State University, Corvallis, Oregon, 97331 USA

2School of Environmental Sciences, University of Guelph, Guelph, Ontario N1G 2W1, Canada 3College of Marine and Environmental DraftSciences, James Cook University, Townsville, QLD 4811, Australia

Corresponding Author: Peter G. Kevan [email protected]

Received; revised; accepted for publication

Running title: Fossil species of Boehmerieae (Ekrixanthera gen. nov.)

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ABSTRACT

The first fossil flowers of Neotropical Urticaceae (Boehmerieae) are described from the

Dominican Republic and Mexico as belonging to a new genus, Ekrixanthera . Ekrixanthera hispaniolae sp. nov. from Dominican amber has pentamerous staminate flowers on short pedicels with a pilose pistillode and heteromorphic pilose tepals, two are clavate and three linear. Ekrixanthera ehecatli sp. nov. has pentamerous staminate flowers lacking pedicels, a pistillode with greatly reduced pilosity, glabrous and heteromorphic tepals with two linear and three wedgeshaped with truncate tips. The presence or absence of a pedicel, heterotrophic condition of the tepals and presence or absence of pilosity of the pistillode and tepals separate the two species. Those characters, together with the pentamerous flowers separate both fossil species from extant genera. The floral Draftstructures indicate explosive pollen release and pollination by wind (anemophily). Pistillate flowers have not been found for this usually dioecious tribe. Lepidopteran herbivory is suggested by a damaged stipule in one specimen and a nymphalid butterfly ( Vanessa like) caterpillar that may have used Ekrixanthera as a food is illustrated. The establish an early lineage of Boehmerieae with characteristic explosive pollen release and perhaps associated herbivorous insects in the West Indies and North America during the midTertiary.

Keywords: palaeobotany, paleoecology, anemophily, Ekrixanthera hispaniolae , Ekrixanthera ehacatli

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INTRODUCTION

Amber is a wonderful medium for preserving delicate structures like flowers and has provided

evidence of various plant lineages dating back to the Earlymid . New World

from the Dominican Republic and Mexico have provided rare glimpses into the flora that existed

in the West Indies during the midTertiary. Genera from the following families of angiosperms

have been described from this New World amber: Poaceae (Poinar and Judziewicz 2005; Poinar

and Columbus 2012), Arecaceae (Poinar 2002a; 2002b), Chrysobalanaceae (Poinar et al. 2008a;

corrected by Chambers and Poinar 2010), Lauraceae (Chambers et al. 2011a; 2012), Meliaceae

(Chambers et al. 2011b; Chambers and Poinar 2012), Burseraceae (Chambers and Poinar 2013),

Myristicaceae (Poinar and Steeves 2013), Rhamnaceae (Chambers and Poinar 2014a),

Ticodendraceae (Chambers and Poinar Draft2014b), (Poinar 1991; Poinar and Brown 2002)

and possibly Moraceae (Poinar et al. 2008b). The Dominican amber forest was characterized by

Poinar and Poinar (1999) based on both animal and plant fossils.

The Urticaceae is a large family with over 45 genera and some 2000 species (Friis 1989;

Wu et al. 2015). The family has a poor fossil record of flowers, with only one definite flower

(Forskohleanthium nudum Conwentz) having been described in Baltic amber (Conwentz 1886).

The present work describes two congeneric species that share characters with other

Boehmerieae, such as Boehmeria, but have characters that prevent assignment to an extant

genus. One species is described from Dominican and the other from Mexican amber. They

represent the first fossil flowers of Neotropical Urticaceae.

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MATERIAL AND METHODS

PROVENANCES

The Dominican amber fossils originated from amber mines in the northern mountain range

(Cordillera Septentrional) of the Dominican Republic between Puerto Plata and Santiago.

Amber from mines in this region was produced by protera Poinar (1991) (Fabaceae).

Dating of Dominican amber is still controversial, with the youngest proposed age of 2015 mya based on Foraminifera (IturraldeVincent and MacPhee 1996) and the oldest of 4530 mya based on coccoliths (Cepek in Schlee 1990). These are considered minimum dates as they are based on microfossils in the strata containing the amber. Most of the amber was secondarily deposited in turbiditic sandstones of the Upper EoceneDraft to Lower Miocene Mamey Group (Draper et al. 1994). Dilcher et al. (1992) stated that “...the amber clasts, from all physical characteristics, were already matured amber at the time of redeposition into marine basins. Therefore, the age of the amber is greater than Miocene and quite likely is as early as late ”. The issue is further complicated by the discovery of Early Oligocene amber in Puerto Rico and Maastrichtian

Paleocene amber in Jamaica (IturraldeVinent 2001) showing that amber from a range of deposits occurs in the Greater Antilles.

The Mexican amber fossils originated from amber mines in the northern mountain ranges or Chiapas Highlands of the Simojovel area in Chiapas, Mexico. Amber from Chiapas, which was produced by Hymenaea mexicana (Fabaceae) (Poinar and Brown 2002), occurs in lignitic beds among sequences of primarily marine calcareous sandstones and silt. The amber is associated with Balumtun Sandstone of Early Miocene and the La Quinta Formation of the Late

Oligocene with radiometric ages from 22.5 to 26 million years (Berggren and Van Couvering

1974). Because the amber was secondarily deposited in these marine formations, it may be

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somewhat older than the above dates.

METHODS

Observations and photographs were made with a Nikon SMZ10 R stereoscopic microscope and

Nikon Optiphot compound microscope with magnifications up to 600 X. Helicon Focus Pro X64

was used to stack photos for better clarity and depth of field.

RESULTS

Three separate pieces of Dominican amber contain fossil representatives ascribed to the tribe

Boehmerieae but not to an extant genus. Dominican amber piece Sd995ADraft contains a single staminate flower (Figs. 13). Dominican amber piece Sd995B contains two staminate flowers, one with the tepals and

stamens beginning to unroll and another with the tepals and stamens outstretched (Fig. 4). The

same piece of amber also contains a developing fruit but not on the same structure (Fig. 5) and

an insectdamaged stipule (Fig. 6) with evidence of putative cystoliths (Fig. 7). Two conjoined

staminate flowers with short pedicels in lateral view (specimen Sd995C) provide indication of

the structure of the inflorescence (Fig. 8).

The Mexican amber piece (Sd996) contains two staminate flowers, one of which is

completely opened (Figs. 9, 10) and another that has the stamens bent back, one of which was

releasing pollen (Fig. 11). We found no evidence of female reproductive structures.

TAXONOMIC PLACEMENT AND DESCRIPTIONS

The specimens we describe (below) belong to species in the tribe Boehmerieae, a large

tribe which, as presently considered, comprises about 20 genera with limits that often are not

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satisfactory. The presence of the pistillode in the staminate flowers of both species we describe indicates that neither can be placed in the tribe Urticeae. With the characters that are preserved in the fossils we describe, we note five similar extant genera in Boehmerieae. We rule out assignment to Nothocnide, Cypholophus and Oreocnide on the basis of stipule forms. Species in the genera Pouzolzia and Boehmeria share greater similarities with the fossils we describe with pentamerous male flowers. In Pouzolzia they are usually vaulted at the apex, at least in Javanese species (Backer and Bakhuizen van den Brink 1965). Staminate flowers of extant species of

Boehmeria are regular (actinomorphic) and most are reported to be tetramerous (Friis 1989), which would separate them from those of the fossils we describe. A persistent filamentous style on the developing fruit is expected for Boehmeria but not necessarily for Pouzolzia (Wilmot

Dear et al. 2009). Even so, the two generaDraft are difficult to distinguish morphologically (Wilmot

Dear et al. 2009). On the basis of morphological and molecular data, members of Boehmeria and Pouzolzia have been assigned to three or two subclades respectively, suggesting polyphyletic origins of both genera (Hadiah et al. 2008; Conn and Hadiah 2009; Wu et al. 2015). The morphological characters defining both genera may be plesiomorphic within at least one of the clades. Because we cannot assign the fossil specimens we describe unambiguously to an extant genus, we propose a new genus, Ekrixanthera , within the tribe

Boehmerieae.

Etymology: The new generic epithet is descriptive of the explosive release of the pollen from the anthers: In Greek Εκρηχικός means explosive and ανθήρας means anther.

Urticaceae: Boehmerieae

Ekrixanthera

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Staminate flowers pentamerous, pistillode present: differs from Pouzolzia by the flowers being

pentamerous and from Boehmeria by the pentamerous flowers rarely found in Boehmeria and the

absence of a persistent filamentous style. The stipule is apiculate.

Ekrixanthera hispaniolae n.sp. (Figs. 1 8)

Description

Specimen in Sd-9-95A (Figs. 13): Staminate flowers pentamerous with very short pedicel and

hairy perianth. Flower diameter 4.4 mm; tepals heteromorphic, 3 linear, 2 clawed; length tepals,

1.7 (1.52.1) mm; width at base, 0.5 (0.40.6) mm; width at tip, 0.8 (0.41.4) mm; stamens

opposite tepals, filament length, 1.4 (1.21.6) mm; anthers twolocular, split longitudinally,

length, 1.1 (0.81.3) mm; pistillode pilose.

Draft

Specimen in Sd-9-95B (Figs. 47): Stipule narrowly ovate, 8.3 mm long, base cordate, tip

pointed, with putative cystoliths present (Fig. 7). Staminate flowers pentamerous with very short

pedicel and hairy perianth. Flower diameter 4.1 mm; tepals heteromorphic, 3 linear, 2clawed;

length tepals, 1.6 (1.41.9) mm; width at base 0.5 (0.40.6); width at tip, 0.9 (0.51.5); stamens

opposite tepals; filament length, 1.5 (1.41.6); anthers twolocular, split longitudinally, length,

0.9 (0.81.1) mm; pistillode pilose; achene glabrous, stigma absent, surrounded by 5 unequal

perianth lobes.

Specimens in Sd-9-95C (Fig. 8). Two staminate pentamerous flowers. Although the floral parts

are coiled and difficult to measure, they appear to have the same features indicated above in

specimens Sd995A and Sd995B. A lateral view shows the short pedicels measuring 0.2 mm

in length (Fig. 8).

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Types: Holotype (accession # Sd995A) (Figs. 13) and Paratypes (Sd995B and Sd995C)

(Figs. 48) deposited in the Poinar amber collection maintained at Oregon State University,

Corvallis, Oregon.

Type locality: Amber mine in the northern mountain ranges (Cordillera Septentrional) of the

Dominican Republic.

Etymology: The specific name reflects the country of origin of the fossil.

Urticaceae: Boehmerieae

Ekrixanthera ehecatli n.sp. (Figs. 911)

Description

Specimen in Sd-9-96: Two pentamerousDraft glabrous staminate flowers lacking pedicels; one open and one partially closed. Measurements for open flower: flower diameter, 3.6 mm; tepals heteromorphic, 2 linear and 3 wedgeshaped; length tepals, 1.2 (0.9 1.3) mm; width at base, 0.5

(0.40.7) mm; width at tip, 0.9 (0.50.9); stamens opposite tepals, filament length, 0.8 (0.70.9) mm; anthers twolocular, split longitudinally, length, 0.8 (0.70.9) mm; pistillode reduced to a few hairs.

Types: Holotype deposited in the Poinar amber collection (accession # Sd996) maintained at

Oregon State University, Corvallis, Oregon.

Type locality: Amber mine in the northern mountain ranges of the Simojovel area in Chiapas,

Mexico.

Etymology: The specific name reflects the evidence for anemophily (Figure 11) and makes reference to the Aztec god of the wind, Ehécatl, also associated with other Náhuatl cultures, including the Maya.

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Comments: E. ehecatli shares the character of heteromorphic tepals with E. hispaniolae .

However in E. ehecatli , only two tepals are linear, while the other three are wedgeshaped rather

than clavate as in E. hispaniolae . The staminate flowers of E. hispaniolae are pubescent but

those of E. ehecatli are glabrous. Pedicels are absent in E. ehecatli but present in E. hispaniolae .

DISCUSSION

The only previous confirmed fossil flower of the Urticaceae is the single Baltic amber

Forskohleanthium nudum Conwentz (Conwentz 1886). The present fossils are the first New

World flowers of the Urticaceae. Actinomorphic (regular) flowers is a basic character of the

Utricaceae (Berg 2004) and it is curiousDraft that in the midTertiary, representatives of the family

existed with heteromorphic flowers (the tepals and sexual forms). It is interesting that Bechtel

(1921) suggested that flowers of Urticales originated from flowers with two whorls of perianth

parts; the heteromorphic tepals in the fossils support that idea. The glabrous condition of the

tepals of E. ehecatli reveals what appears to be a basal whorl of two linear tepals under a

separate whorl of wedgeshaped tepals when viewed from below (Fig. 10).

Explosive pollen release is a characteristic of the family (see MontoyaPfeiffer et al.

2016) and is demonstrated in the flower of E. ehecatli that has a burst of pollen adjacent to the

anther. Such explosive “bursts” propel the pollen into the air to be conveyed by wind and

atmospheric turbulence to receptive pistillate flowers on the same (monoecy) or different

(required for dioecy) , thus permitting pollination. Details of anemophily in Boehmeria

caudata Sw., and other plants with explosively released pollen in Urticaceae and other families

are provided in the preceding paper (MontoyaPfeiffer et al. 2016). Unfortunately, we cannot

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comment on the breeding system (monoecy vs. dioecy) in the fossil plants we describe because pistillate flowers are poorly represented and in the single example (Fig. 5) of both floral sexes being present in the same sample of amber, they are not structurally unified.

Several insects were associated with the flowers of E. hispaniolae . A small and incomplete caterpillar was near the stipule that showed evidence of insect damage (Fig. 12). The fossil shown in Fig. 12 is morphologically very similar to a previously collected caterpillar in

Dominican amber that has been identified as a prototypic extinct ancestor of the Nymphalidae

Pycina Vanessa linkage that is considered to belong to the Urticaceaefeeding tribe Nymphalini

(Fig. 13). Today caterpillars of Vanessa Fabricius and the related Hypanartia Hübner are the only butterflies that feed on Urticaceae in Hispaniola (Hammond and Poinar 1998).

Several adult gall midges (Diptera:Draft Cecidomyiidae) were adjacent to the female flower.

Gall midges are known to develop in stem galls of Boehmeria in North America (Gagné 1989). It is possible that the fossil gall midges had a similar relationship with E. hispaniolae . An ant belonging to the subfamily Dolichoderinae was adjacent to one of the male flowers (see also antenna in Figure 4).

ACKNOWLEDGEMENTS

We thank the students (MontoyaPfieffer et al. 2016) on the International Pollination Course at

Intervales State Park, São Paulo, Brazil in December 2014 for being the catalysts for this submission. It was through their study on Boehmeria caudata followed by the suggestion of

Peter Bernhard of St. Louis University and friendship between BJ and PGK that we came together. GP thanks Cesare Baroni Urbani for determination of the ant in Sd995B. PGK thanks the Canadian Natural Sciences and Engineering Research Council for help in funding preparation and publication of this paper.

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Draft

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Figure Captions

Figure 1. Top view of staminate flower of Ekrixanthera hispaniolae n. sp. in Dominican amber.

Specimen Sd995A. Scale bar = 1.0 mm.

Figure 2. Detail of underside of staminate flower of Ekrixanthera hispaniolae n. sp. in

Dominican amber. Specimen Sd995A. Scale bar = 0.4 mm.

Figure 3. Detail of center of staminate flower of Ekrixanthera hispaniolae n. sp. in Dominican amber showing pilose pistillode. Specimen Sd995A. Scale bar = 0.3 mm.

Figure 4. .Top view of second staminateDraft flower of Ekrixanthera hispaniolae n. sp. in Dominican amber. Ant’s (Hymenoptera: Formicidae: subfamily Dolichoderinae) antenna is preserved with the flower (bottom of picture). Specimen Sd995B. Scale bar = 0.6 mm.

Figure 5. Developing fruit of Ekrixanthera hispaniolae n. sp. in Dominican amber. Note the lack of persistent style. Specimen Sd995B. Scale bar = 1.9 mm.

Figure 6. Stipule of Ekrixanthera hispaniolae n. sp. in Dominican amber. Note damage (arrow), probably from feeding caterpillar preserved in the same piece of amber (Figure 12). Specimen

Sd995B. Scale bar =1.3mm.

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Figure 7. Leaf upper surface of Ekrixanthera hispaniolae n. sp. in Dominican amber showing

putative cystoliths (arrow). Specimen Sd995B. Scale bar = 62 µm.

Figure 8. Lateral view of two staminate flowers of Ekrixanthera hispaniolae n. sp. in Dominican

amber. Specimen Sd995C. Arrows indicate short pedicels. Scale bar = 1.0 mm.

Figure 9. Top view of staminate flower of Ekrixanthera ehecatli n. sp. in Mexican amber. The

pistillode is reduced to a few hairs. Specimen Sd996. Scale bar = 0.8 mm.

Figure 10. Underside of staminate flower of Ekrixanthera ehecatli n. sp. in Mexican amber.

Specimen Sd996. Scale bar = 0.7 mm.Draft

Figure 11. Freezeframe fossilized release of pollen from an anther of Ekrixanthera ehecatli n.

sp. in Mexican amber. Specimen Sd996B. For discussion on explosive release of pollen from

Boehmerieae, see MontoyaPfeiffer et al. (2016) and associated video clip. Scale bar = 0.3 mm.

Figure 12. A caterpillar associated directly with the damaged stipule in Figure 6. The specimen is

too incomplete to assign it to Nymphalidae. Specimen Sd995B from the Poinar collection

contains both the stipule and this caterpillar. Scale bar = 0.6mm.

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Figure 13. A nymphalid butterfly caterpillar identified as a prototypic extinct ancestor of the

Nymphalidae Pycina Vanessa linkage that is considered to belong to the Urticaceaefeeding tribe

Nymphalini ( Specimen L-3-36 from the Poinar collection). The fossil shown in Figure 12, although not so well preserved, is similar enough to be worth note. Caterpillars of Vanessa

Fabricius and the related Hypanartia Hübner are the only butterflies that feed on Urticaceae in

Hispaniola today (Hammond and Poinar, 1998). Scale bar = 2.3 mm.

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