There are only two ways into Aguas Calientes, Peru: by train or on foot.

We opted for the train.

Departing from Ollantaytambo, we meandered through the Sacred Valley, following the Urubamba River beneath towering, snow-capped Andean peaks. The landscape was nothing short of spectacular. As the mountains closed in around us, the valley grew increasingly lush, and before long, we arrived in the little town nestled beneath one of the most recognizable archaeological sites on Earth.

Machu Picchu.

But we weren't just here for the ruins.

During our previous expedition in 2023, we documented a particularly fascinating population of the wild Andean pepper species Capsicum geminifolium.

What made this population so interesting?

Its flowers.

Unlike the more commonly encountered forms of this species, these plants produce beautiful, entirely yellow corollas, with a slightly campanulate (bell-shaped) appearance and remarkably elongated calyx appendages.

A striking combination of characteristics that immediately caught our attention during our first visit.

And we wanted to see them again.

After arriving in Aguas Calientes, we wasted no time. The following morning, we boarded one of the buses that climb the seemingly endless switchbacks toward Machu Picchu.

As we ascended through the clouds, the town grew smaller beneath us. From the archaeological site above, we could look across the valley and identify the very mountainside where we had documented these plants three years earlier.

I even managed to get a photograph pointing directly toward our previous observation site from atop Machu Picchu!

But the real excitement came when we returned to the population itself.

Not only were the same specimens still growing where we had documented them in 2023, but an incredible number of additional plants had established themselves along the southern and southeastern base of the opposing mountain.

What had previously been a handful of fascinating observations had become a sea of Capsicum geminifolium.

Plants were growing along the steep slopes, emerging from the surrounding vegetation and occupying pockets of suitable habitat above the Urubamba River.

And those flowers!

The same beautiful, entirely yellow corollas. The same slightly bell-shaped appearance. The same exaggerated calyx appendages that made this population so memorable.

Seeing these characteristics expressed across so many individuals was especially exciting.

For those interested in observing this population, the plants can be found along the lower slopes opposite Machu Picchu, near the railway corridor outside Aguas Calientes. The area is accessible by following the road toward the Machu Picchu entrance and exploring the publicly accessible footpaths in the surrounding area.

A word of caution, however: trains pass through this corridor regularly. Remain on designated paths, stay well clear of the tracks, and never allow your attention to the plants to distract you from your surroundings.

We certainly had a reminder of just how active this railway is.

While photographing one particularly beautiful specimen, an approaching train appeared in the background, its headlights illuminating the tracks behind the plant.

A wild Capsicum geminifolium, growing beneath the towering mountains of Machu Picchu, with a train emerging through the valley behind it.

One of my favorite photographs from this entire expedition.

For me, returning to a wild population years after its initial discovery is every bit as rewarding as finding something new.

You get to ask questions that a single visit simply cannot answer.

Are the original plants still alive? Has the population expanded? Are the same morphological characteristics being expressed in subsequent generations? How has the surrounding habitat changed?

In this case, we were fortunate enough to observe what appears to be a thriving population, with considerably more plants than we documented during our previous visit.

And perhaps most importantly, this little corner of the Andes continues to remind us just how much there is left to learn about wild Capsicum.

Three years later, and these beautiful yellow flowers are still waiting for us beneath Machu Picchu.

Capsicum geminifolium — Aguas Calientes, Peru.

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