2. Echinocactus humilis Philippi

A Chilean Endemic with Primarily Juvenile Stems By P. C. Hutchison¹

Echinocactus humilis Philippi was originally described in 1860. This description is inadequate and it has not been possible, in the absence of specimens, for subsequent authors to place the taxon in any of the genera now considered to encompass the echinocactoid species of Chile. The original description from Florula Atacamensis in Dr. R. A. Philippi's "Viage al Desierto de Atacama," 197, 1860, reads:

"138. Echinocactus humilis Ph. E. parvus, subglobosus, depressus, circa 12 lin. latus, 10 lin. altos; costis circa 10-12; verrucis superioribus aculeos circa 10, cinereos, setaceos gerentibus, quorum peripherici divaricati, centralis credos; parum major, 12 lin. altos; aculeis verrucarum basalium vix 1½ lin. longis, setaceis ; corolla sulphurea, 9 ½ lin. longa.

Prope Paposo in detritu rupium ad pedes montium litoralium crescit."

Subsequent authors have added little information. Britton and Rose in Cactaceae 3: 89, 1922, suggested that this species might belong to their genus Copiapoa. Rose could not find the type at the Philippi Herbarium (Museo National de Historia Natural, Santiago, Chile). My studies there likewise did not disclose a specimen. Presumably the type has not been preserved.

The type locality, Paposo, is on the coast of Province Antofagasta, Chile, about 50 km. north of the port of Taltal. I collected in this region in January, 1952, and found this species abundant in restricted areas near the road which swings up the coastal hills above Paposo. It is difficult to find because it grows partially buried in soil which it matches in color. The following description is compiled from field notes and studies of preserved as well as newly imported plants in cultivation at this botanical garden.

Copiapoa humilis (Philippi) P. C. Hutchison, comb. nov.
Echinocactus humilis Phil. in Fl. Atac., 197, 1860, non Pfeiffer, 1837.²

Plant with a tuberous root 15 cm. or more long and ca. 5 cm. diam., root apex rounded or flattened. Mature plant solitary or caespitose, stem subglobose, glaucous green, usually connected to root apex by a narrowly constricted stern elongation 5 to 10 mm. in diam. and ±4 cm. long. Stem 5 to 7 cm. diam., 4 to 6 cm. high, ribs obscure, 8 to 12, tuberculate. Areoles grey-felted, spines grey, straight or slightly curved, radial spines 10 to 1/1, 5 to 15 mm. long, spreading to suberect, central spines 1 to 4, erect, porrect or barely decurved, 1.0 to 2.5 cm. long, darker apically. Flowers apical, lower third submerged in dense, grey, apical wool, campanulate, 3 cm. (2 cm. in type!) long, outer perianth segments yellow with a rose midstripe which on lower segments is broader, lowest seg­ments rose narrowly margined yellow, inner segments dark yellow. Filaments, anthers and style dark yellow, stigma orange-yellow. Style 2.0 cup. long, lobes 9, 3 trim. long, minutely papillose, slightly exserted. Fruit semiglobose, truncate, 9 mm. diam., 8 nun. tall, with a single subapical ovate-acute scale 2 mm. broad and 3 mm. long, bright red.

Chile, Prov. Antofagasta, Dept. Taltal, coastal hills above Paposo, P. C. Hutchison 405 (UC).

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Immature plants, or at least immature stems on mature roots constituted about 90 % of the population at the type locality. These differ greatly from mature stems in most characteristics. A description of them is essential since the original description seems to combine characters of both immature and mature stages of growth, and since immature stems are likely to be collected in the future or may already be represented in some herbaria.

Immature stems semiglobose, 1 to 3.5 cm diam. and tall, length and breadth usually equal, spines straight, radial spines ca. 10, setacious, spreading, 2 to 5 mm. long, tan-grey or grey, central spine lacking or 1, suberect to porrect, to 1.1 cm. long, grey.

In cultivation many of the characteristics of C. humilis may change. Thus, at the University of California Botanical Garden (Berkeley), under glass, areolar and apical wool may be tan in color and may be more profuse; epidermis may be green or purple-green and glabrous; radial spines on immature stems are usually straw-colored with brownish tips; central spines are brown on immature, and black on mature stems. Further phenotypic changes will un­doubtedly appear. The species can be grafted readily, but unless placed on a slow-growing stock, becomes abnormally bloated.

In nature the caespitose habit may arise in several ways. An old plant may form basal offsets as its main stem begins to decline. When decline is rapid these offsets may not survive and the entire aerial stern dies. The root, however, may remain alive and from its crown send up elongated narrow growths to the soil surface 3 to 6 cm. above the root crown. These growths, because they bear aborted areoles at an early stage, are clearly cauline. When such a growth reaches the surface, a normal aerial plant stem develops. A root may form one or many such stems. These may arise from the root crown or from a former persistent stem-elongation. If this underground stem-elongation of the dying aerial plant stem persists, a new plant usually forms at its apex, and additional offsets may arise from its apex, from below it, from the root crown or from any combination of these, or not at all.

Thus it can readily be seen that the apparent maturity of the above ground stem is not a true indication of the age of the plant. It is indeed probable that the root and hypogean stem survive through the maturation of many generations of aerial stems.

Immature aerial stems occasionally form lateral fibrous roots in nature, and do so readily in cultivation. If the parent root dies these stems lose their attachment to it and each becomes established as in independent plant.

Fig.24. Copiapoa humilis excavated plants showing mature tuberous roots, elongated necks and immature stems, ca. x 0.5. (Right) Copiapoa humilis immature stems in habitat, about x 0.3, clearly visible after slight surface excavation, showing 11 stems.

Copiapoa humilis survives under extremely adverse environmental conditions.

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Desiccation by coastal winds, intense insolation and high temperatures and slight to no precipitation as well as the attack of an insect parasite³ reduce the likelihood of flower formation. All plants of Copiapoa taltalensis (Werdermann) Looser, a closely related species, which I examined in its area 100 km. to the south, were infested but apparently few of them were killed and the presence of the parasite did not inhibit flowering or fruiting. The larva apparently matures inside the plant body and consumes the parenchyma tissue. If the same or a similar species of beetle were to attack C. humilis, which is less than half the diameter of C. taltalensis it would attack only the most mature stems, as a small stem would not provide sufficient food to bring a larva to maturity. This might account for the fact that no immature stems or any of the smallest mature stems showed indications of insect damage, yet of the three large stems found, all were attacked. Two of them were dying and the third was nearly dead although it was flowering sparsely and had formed one fruit. The smaller mature (?) stems had formed apical wool and typical longer, stouter spines, but none was found in flower or with evidence of a previous year's flowering.

In nature few plants appear ever to attain flowering size. In addition to insect depreda­tions the physical environment inhibits growth. The primary source of water for plants along this part of the Chilean coast is winter fog. The lower limit of fog, as shown by the luxuriant growth of epiphytes on cacti and shrubs at higher altitudes, is above the upper limit of this species. C. humilis, therefore, must receive much less water from condensation of fog than is available to plants higher up, and only in exceptional years, through lowering of the fog belt perhaps, or occurrence of a slight rain, would it receive an increase in water supply. It probably reaches maturity much more slowly than plants in the fog belt and then would be subject to attack by the larvae under conditions previously described. Even if the plant succeeds in flowering and forming seed prior to stem decay induced by the attack of the borer, climatic conditions would usually not permit survival of seedlings if germination could take place. In other words, sexual reproduction of C. humilis must be much reduced in its natural state. Nevertheless, the mode of growth and vegetative reproduction of the species enables it to survive and the size of the population is not necessarily reduced by its failure to reproduce sexually.

In Copiapoa tuberous roots are common in many species. So far as known, C. humilis is unique in the genus for an attenuated neck connecting the stem to the root; in the tribe Echinocactanae for its ability and indeed dependence on vegetative reproduction for survival; in the family Cactaceae for the predominance of immature stem growths in nature (90% versus less than 1% in all other species and genera studied in the field).

The nature of these anomalies in C. humilis gives rise to a number of interesting questions. What is the species of insect which attacks this plant and what inter-relationships, if any, exist between their respective life-cycles and climate? Will the plant bloom freely and set viable seed in cultivation ? Will it reproduce its peculiar morphological attributes if grown from seed or from cuttings? If, by contrast, a tuberous root develops, will it form before or after the plant stem becomes mature? The answers to certain of these questions may suggest an explanation of the morphological anomalies of this species in terms of the relative significance of environmental and genetic factors involved.

C. humilis is apparently more closely related to C. taltalensis than to any other presently known Copiapoa. The latter species occurs in the Sierra Esmeralda, a low range of coastal hills about 100 km. south of Paposo. I did not find plants of either species between these two localities. Apparently both are narrow endemics.