# Floral Scent Variation in the Heterostylous Species _Gelsemium sempervirens_
## 1 Introduction  
Flowering plants often produce attractants for pollinators in the form of scent [1; 2; 3; 4], color [5], and nectar [6]. The scent profile of a flower may be due to petals, sepals, anthers, stigmas, and nectries [7; 8; 9; 10; 11] and is composed of many different volatile organic compounds (VOCs). These VOCs are natural lipophilic products that have relatively low molecular weights (30-300 amu) and high vapor pressures, allowing easy detection at ambient temperatures [12]. Different parts of the plant emit VOCs, but the flowers typically emit the largest portion of scent from a plant [13]. Floral scent compounds promote cross-pollination and reproduction of flowers by attracting insect and other animal pollinators [14], who are rewarded with nectar and nourishment as pollinators help to distribute pollen amongst flowers. Over 1700 floral scent compounds [12] have been determined for a variety of plant species and are comprised of terpenids (molecules derived from isoprene), benzenoids (molecules containing a benzene ring), fatty acid derivatives (aliphatic molecules with 1 to 25 carbon atoms), and yeast associated compounds (metabolic by-products such as ethanol), all with a variety of functional groups including alkanes, alkenes, aldehydes, ketones, alcohols, carboxylic acids,and esters [15]. The intensity and distribution of these scent compounds work together with visual and other cues to attract specific pollinators to a flower [14]. A typical floral bouquet is comprised of 20 to 60 compounds emitted between 1 pg and 30 \(\upmu\)g per hour [15]. The compounds produced can vary between flower populations, style morphs, flower and plant tissues, time of day (light), temperature, and herbivory events (reviewed in [16]). Although floral scent has been well characterized in several plant families [12], none of the scent profiles of flowering plants within Gelsemiaceae have been examined. _Gelsemium sempervirens_ (L) W.T. [PERSON], commonly known as yellow jessamine or Carolina jessamine, is a toxic, perennial, distylous woody vine of the family Gelsemiaceae, which is only comprised of three genera [17; 18]. _G. sempervirens_ is indigenous to the Piedmont and coastal areas of the southeastern United States [19], and its flowers produce nectar and are pollinated by a variety of bee species [20; 21]. This plant has been cultivated since the mid-17 th century [19] and is known for its fragrant aroma, but also for the toxicity of its nectar, flowers, and other plant parts [19; 22]. The medicinal and toxicological properties result from the presence of gelsemine and other alkaloids in plants from the genus _Gelsemium_, which have been widely studied and characterized [23; 24]. The alkaloids in _G. sempervirens_ act as deterrents for antagonists who consume nectar, flower petals, and reproductive structures without pollinating the plant [20]. Higher nectar gelsemine levels have been correlated with fewer visitations and reduced pollen transfer between flowers [20; 21]. It has been suggested that _G. sempervirens_ evolved to bloom in early spring, when there is little competition for pollinators from other flowering plants, in order to counteract its toxicity and ensure its reproductive success [25]. The tubular shaped hermaphroditic flowers exist in two distinct forms that are self-incompatible within plant and style morph. The pin morph, also referred to as the L styled morph, has long styles with the stigmas protruding from the opening of the tubular flower and short stamens that remain within the floral tube (Figure 1a). The thrum morph, also referred to as the S styled morph, has short styles with long anthers protruding from the opening of the flower (Figure 1b) [26]. While it has been shown that flowers of the S morph are on average larger (S corollas are 11% longer and 26% wider than L corollas) [27; 28] and contain on average higher levels of gelsemine than the L morphs [26], it is unknown whether floral scent varies between the L and S morphs.