Carica candicans is a wild relative of papaya (Carica papaya L.). Although the fruits are not marketed, they are occasionally consumed by the local population, and some market vendors and healers interviewed did know the plant under its vernacular name, "mito." Larco 12 never mentions the plant in relation to Ulluchu. Assuming that he indeed encountered a plant with that name, it cannot have been C. candicans, because this species would have been named "mito."

McClelland 6 argues that Ulluchu "cannot be a papaya, which belongs to a group of plants called 'cauliflory' [i.e., stem flowery]. ... The flowers and fruit of a cauliflory grow on the trunk of the tree and not on the limbs. ... Ulluchus depicted in Moche art, however, hang from limbs. Papaya leaves do not resemble ulluchu leaves, which are triangular, ovoid, or boomerang shapes hanging from limbs. Each large palmate papaya leaf grows on a stem from the top of the tree." However, further complicating this matter, it turns out that C. candicans happens to be one of the few papayas that are not cauliflorous, that have triangular leaves with entire margins, and the fruits do hang from branches. Thus, judging from the iconography alone, C. candicans actually could be Ulluchu.

Based on recent archaeological evidence however, 68923, it has become clear that the actual fruits found in burials do not resemble C. candicans. In addition, the explanation that papain, might have been extracted by the Moche from unripe papaya for use as a blood anti-coagulant 5, albeit reasonable, does not make much sense from a phytochemical perspective. Cultivated papaya (C. papaya) is often depicted in Moche pottery, and the species contains large amounts of papain. Why would the Moche have resorted to a rare wild species, when they could have used a cultivar with the same properties that grew on their very doorstep? Also, C. candicans fruits are often 10–15 cm. long, and, while this would relate to the size of some of the Ulluchus in the iconography, it is vastly larger than many of the fruits depicted and much larger than the fruits found in burials. Finally, the anatomy of C. candicans simply does not correlate with the fruits encountered in burials.

Moche fine-line drawings of Ulluchu normally depict seed pods or seeds floating in the air in sacrificial scenes (e.g., 6 Fig. Three.14), associated with runners and messengers (e.g., 6: Fig. Three.1) or intoxicated priests (e.g., 6: Fig. Three.6). The Ulluchu fruits vary greatly in size, ranging from about 1–15 cm. They are normally comma-shaped, often with an "exaggerated round calyx" [6: 43] with lines on the body of the fruit (e.g., 6: Fig. Three.4). Some illustrations show Ulluchu harvested by monkeys, and in such cases the fruit is mostly shown growing along the axes of the plant's leaves (e.g., 6: Figs. Three.27 & Three.28).

Starting from this basis in 2002, we built on the work of Donna McClelland and the archaeological excavations at Sipán in the Lambayeque Valley 8924 and at Dos Cabezas in the Jequetepeque Valley in the 1990s 623. Botanically, all these depictions resemble capsules or drupe-like fruits. It became apparent that in a biodiversity hotspot like Peru, with a flora of more than 18.000 species, a large number of plant families have fruits that vaguely resemble Moche fineline drawings of Ulluchu, and many of these families contain more than one genus with similar fruits. Examples include: (Apocynaceae: Ambelania; Caricaceae: Carica; Celastraceae: Maytenus; Chrysobalanaceae: Chrysobalanus, Hirtella, Licania; Convolvulaceae: Dicranostyles; Fabaceae: Aldina, Alexa, Andira, Dipteryx, Dussia, Ormosia; Guttiferae: Tovomita; Hippocrateaceae: Cheiloclinum, Salacia; Icacinaceae: Calatola; Meliaceae: Guarea; Menispermaceae: Abuta, Curarea, Elephantomene, Telitoxicum; Myristicaceae: Virola; Olacaceae: Cathedra; Quiinaceae: Lacunaria; Sabiaceae: Meliosma; Sapindaceae: Cupania, Paullinia; and Sapotaceae: Pouteria. Some of these are still highly important in traditional societies. For example, Ambelania fruit is often consumed; Ormosia contains potent poisonous compounds, but is now mostly used in crafts; Curarea is one of the ingredients of "curare," the famous Amazonian arrow poison; Virola species are still used as potent snuffs in the Amazon; and Paullinia is the source of "yopo," an important stimulant. However, none of these carry the vernacular name Ulluchu.

Fortunately, at this time the archaeological evidence provides good clues for identification. The Ulluchu fruits found in burials in the 1990's are clearly capsules or drupes, slightly comma-shaped, between 1.5 and 5 cm. long, and slightly grooved (Fig. 1A&1B). They closely resemble bone, gold, and Spondylus beads found in situ in size, form, and texture (Fig. 1C–E). In the iconography, the fruits are often depicted on both sides of branches, as in the headdress of Fig. 1F. It is important to note that this figure has widely extended nostrils, as is often seen in people inhaling hallucinogenic snuffs, and is holding a gourd and pestle. McClelland (6: Fig. Three.18) interpreted this as lime gourd used for chewing coca. We suggest that this might also be a gourd used to grind the seeds of Ulluchu for inhalation. Further iconographic evidence supports this hypothesis. Runners and messengers associated with Ulluchu are often winged – they literally fly, i.e., the inhalation of Ulluchu gives them wings. An excellent example is the runner depicted in Fig. 1G: The personage has Ulluchu on his belt, Ulluchu seeds floating above its head, and an instrument in his hand that closely resembles a typical double snuff tube that would serve to inhale powdered hallucinogenic substances. Thus, it seems possible that one of the uses of Ulluchu may have been as a mind-altering snuff. Another reason for identifying the seeds in the iconography as hallucinogenic Ulluchus is underscored by Fig. 1H: This is part of a famous Moche scene (see 6: Fig. Three.34) where monkeys are picking fruits from an Ulluchu tree. It is important to note that the tree depicted has opposite leaves and that seeds are extracted from the fruit, possibly for roasting in a typical oven on the bottom right. The roasted seeds could then be ground to powder and inhaled. The fruits themselves seem to be 5-valved. The function of Ulluchu as a hallucinogen is reinforced by other imagery (e.g., 6: Fig. Three.6), where personages, surrounded by Ulluchu fruits lie on the ground in what clearly appears to be an intoxicated state. In addition, prisoners in sacrificial scenes (e.g., 25: Figs. Two.2, Two.3, Two.12 & Two.24), especially the well known "lines of prisoners" at Huaca El Brujo and Huaca de la Luna (Fig. 2) all show clearly visible erections, which may be seen as another indication of the ingestion of some substance causing this effect. From this perspective Larco's term Ulluchu 2, if derived from Quechua "ullu-uchu" – "penis pepper," would in fact make sense in describing the possible effects of the plant in question. Also, the association with sexual arousal is reinforced by mythical scenes where an Ulluchu tree grows out of the back of an erotic couple.

In light of the above, Ulluchu is a tree with opposite leaves and fruits that are drupes between 1–15 cm long possibly containing active ingredients that would elevate the blood pressure and cause erections, and psycho-active substances. The only plant family from the list above having representatives that meet all these criteria is Meliaceae, and the genus Guarea is the one that most closely fits the description. It includes mostly trees with pinnate leaves (which is unusual for Meliaceae), and fruits that are 3–5 valved capsules, with large, pseudo arillate seeds. The genus Guarea is found throughout Peru, but is mostly restricted to tropical lowland forests, with some species reaching cloud forest habitat. No species is found along the dry coast of Peru, which indicates that the material must have been widely traded in Moche times. A typical representative is Guarea grandifolia DC. The species has clearly pinnate leaves (Fig. 3A), and the fruits (Fig. 3C) very clearly resemble the archaeological samples depicted in Fig. 1. In addition, Guarea contains a large number of species with varying fruit sizes (from 1–15 cm.), calyx swelling, and grooving on the body of the fruit (Fig. 4), which all correlates with the varied Ulluchu imagery in Moche fineline drawings. The seeds of Guarea species, with a distinct white navel, very much resemble the seeds depicted in Moche fineline paintings.

Many species of Guarea are known by a wide variety of vernacular names, e.g., Guarea spec.: requia, kushímsakish; G. glabra: yecheñor, yechemor; G. grandifolia: bola requia; G. guidonia: atapio, latapi, latapi caspi, requia colorada, requia latapi, xoro; G. kunthiana: requia, paujil ruro; G. purusana: latapi, requia). The wood of many species is used as timber for construction. The wood, bark, and leaves contain compounds that act as abortive, emetic, purgative, and antiamoebiac agents, and the bark is often sold as Coccilliana in expectorant preparations 12262728. The fruits and seeds contain a variety of alkaloids that are very rarely used due to their high toxicity 29. Some of the alkaloids found, e.g. rusbyine, have a structure and effects like emetine, an alkaloid found in Psychotria ipecacuanha (Brot.) Stokes, which has been widely used as an emetic and expectorant. Other species of Psychotria are well known as components in ayahuasca preparations due to their high content of N,N-DMT 30. In large dosages, ipecac preparations cause high blood pressure, arrhythmia, spasms, and extension of the blood vessels. While the existing literature on Guarea seed compounds is rather fragmentary, it seems clear that a concentrated dosage of Ulluchu seeds, if ingested, would increase a prisoner's heartbeat, elevate the blood pressure, and widen blood vessels thus causing erection. All of this would make it much easier to extract sacrificial blood. Also, when inhaled by priests, the active compounds could have a mind-altering effect, which would not necessarily lead to high levels of toxicity, and could induce very rapid, short-term hallucinations.